Move JS libs in the libs subdir

1 files changed, 7725 insertions, 0 deletions

diff --git a/hyperkitty/static/js/libs/protovis-d3.1.js b/hyperkitty/static/js/libs/protovis-d3.1.js
new file mode 100644
index 0000000..af56eac
--- /dev/null
+++ b/hyperkitty/static/js/libs/protovis-d3.1.js
@@ -0,0 +1,7725 @@
+/**
+ * @class The built-in Array class.
+ * @name Array
+ */
+
+if (!Array.prototype.map) {
+  /**
+   * Creates a new array with the results of calling a provided function on
+   * every element in this array. Implemented in Javascript 1.6.
+   *
+   * @see <a
+   * href="https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/Map">map</a>
+   * documentation.
+   * @param {function} f function that produces an element of the new Array from
+   * an element of the current one.
+   * @param [o] object to use as <tt>this</tt> when executing <tt>f</tt>.
+   */
+  Array.prototype.map = function(f, o) {
+      var n = this.length;
+      var result = new Array(n);
+      for (var i = 0; i < n; i++) {
+        if (i in this) {
+          result[i] = f.call(o, this[i], i, this);
+        }
+      }
+      return result;
+    };
+}
+
+if (!Array.prototype.filter) {
+  /**
+   * Creates a new array with all elements that pass the test implemented by the
+   * provided function. Implemented in Javascript 1.6.
+   *
+   * @see <a
+   * href="https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/filter">filter</a>
+   * documentation.
+   * @param {function} f function to test each element of the array.
+   * @param [o] object to use as <tt>this</tt> when executing <tt>f</tt>.
+   */
+  Array.prototype.filter = function(f, o) {
+      var n = this.length;
+      var result = new Array();
+      for (var i = 0; i < n; i++) {
+        if (i in this) {
+          var v = this[i];
+          if (f.call(o, v, i, this)) result.push(v);
+        }
+      }
+      return result;
+    };
+}
+
+if (!Array.prototype.forEach) {
+  /**
+   * Executes a provided function once per array element. Implemented in
+   * Javascript 1.6.
+   *
+   * @see <a
+   * href="https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/ForEach">forEach</a>
+   * documentation.
+   * @param {function} f function to execute for each element.
+   * @param [o] object to use as <tt>this</tt> when executing <tt>f</tt>.
+   */
+  Array.prototype.forEach = function(f, o) {
+      var n = this.length >>> 0;
+      for (var i = 0; i < n; i++) {
+        if (i in this) f.call(o, this[i], i, this);
+      }
+    };
+}
+
+if (!Array.prototype.reduce) {
+  /**
+   * Apply a function against an accumulator and each value of the array (from
+   * left-to-right) as to reduce it to a single value. Implemented in Javascript
+   * 1.8.
+   *
+   * @see <a
+   * href="https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/Reduce">reduce</a>
+   * documentation.
+   * @param {function} f function to execute on each value in the array.
+   * @param [v] object to use as the first argument to the first call of
+   * <tt>t</tt>.
+   */
+  Array.prototype.reduce = function(f, v) {
+      var len = this.length;
+      if (!len && (arguments.length == 1)) {
+        throw new Error("reduce: empty array, no initial value");
+      }
+
+      var i = 0;
+      if (arguments.length < 2) {
+        while (true) {
+          if (i in this) {
+            v = this[i++];
+            break;
+          }
+          if (++i >= len) {
+            throw new Error("reduce: no values, no initial value");
+          }
+        }
+      }
+
+      for (; i < len; i++) {
+        if (i in this) {
+          v = f(v, this[i], i, this);
+        }
+      }
+      return v;
+    };
+}
+/**
+ * @class The built-in Date class.
+ * @name Date
+ */
+
+Date.__parse__ = Date.parse;
+
+/**
+ * Parses a date from a string, optionally using the specified formatting. If
+ * only a single argument is specified (i.e., <tt>format</tt> is not specified),
+ * this method invokes the native implementation to guarantee
+ * backwards-compatibility.
+ *
+ * <p>The format string is in the same format expected by the <tt>strptime</tt>
+ * function in C. The following conversion specifications are supported:<ul>
+ *
+ * <li>%b - abbreviated month names.</li>
+ * <li>%B - full month names.</li>
+ * <li>%h - same as %b.</li>
+ * <li>%d - day of month [1,31].</li>
+ * <li>%e - same as %d.</li>
+ * <li>%H - hour (24-hour clock) [0,23].</li>
+ * <li>%m - month number [1,12].</li>
+ * <li>%M - minute [0,59].</li>
+ * <li>%S - second [0,61].</li>
+ * <li>%y - year with century [0,99].</li>
+ * <li>%Y - year including century.</li>
+ * <li>%% - %.</li>
+ *
+ * </ul>The following conversion specifications are <i>unsupported</i> (for now):<ul>
+ *
+ * <li>%a - day of week, either abbreviated or full name.</li>
+ * <li>%A - same as %a.</li>
+ * <li>%c - locale's appropriate date and time.</li>
+ * <li>%C - century number.</li>
+ * <li>%D - same as %m/%d/%y.</li>
+ * <li>%I - hour (12-hour clock) [1,12].</li>
+ * <li>%j - day number [1,366].</li>
+ * <li>%n - any white space.</li>
+ * <li>%p - locale's equivalent of a.m. or p.m.</li>
+ * <li>%r - same as %I:%M:%S %p.</li>
+ * <li>%R - same as %H:%M.</li>
+ * <li>%t - same as %n.</li>
+ * <li>%T - same as %H:%M:%S.</li>
+ * <li>%U - week number [0,53].</li>
+ * <li>%w - weekday [0,6].</li>
+ * <li>%W - week number [0,53].</li>
+ * <li>%x - locale's equivalent to %m/%d/%y.</li>
+ * <li>%X - locale's equivalent to %I:%M:%S %p.</li>
+ *
+ * </ul>
+ *
+ * @see <a
+ * href="http://www.opengroup.org/onlinepubs/007908799/xsh/strptime.html">strptime</a>
+ * documentation.
+ * @param {string} s the string to parse as a date.
+ * @param {string} [format] an optional format string.
+ * @returns {Date} the parsed date.
+ */
+Date.parse = function(s, format) {
+  if (arguments.length == 1) {
+    return Date.__parse__(s);
+  }
+
+  var year = 1970, month = 0, date = 1, hour = 0, minute = 0, second = 0;
+  var fields = [function() {}];
+  format = format.replace(/[\\\^\$\*\+\?\[\]\(\)\.\{\}]/g, "\\$&");
+  format = format.replace(/%[a-zA-Z0-9]/g, function(s) {
+      switch (s) {
+        // TODO %a: day of week, either abbreviated or full name
+        // TODO %A: same as %a
+        case '%b': {
+          fields.push(function(x) { month = {
+                Jan: 0, Feb: 1, Mar: 2, Apr: 3, May: 4, Jun: 5, Jul: 6, Aug: 7,
+                Sep: 8, Oct: 9, Nov: 10, Dec: 11
+              }[x]; });
+          return "([A-Za-z]+)";
+        }
+        case '%h':
+        case '%B': {
+          fields.push(function(x) { month = {
+                January: 0, February: 1, March: 2, April: 3, May: 4, June: 5,
+                July: 6, August: 7, September: 8, October: 9, November: 10,
+                December: 11
+              }[x]; });
+          return "([A-Za-z]+)";
+        }
+        // TODO %c: locale's appropriate date and time
+        // TODO %C: century number[0,99]
+        case '%e':
+        case '%d': {
+          fields.push(function(x) { date = x; });
+          return "([0-9]+)";
+        }
+        // TODO %D: same as %m/%d/%y
+        case '%H': {
+          fields.push(function(x) { hour = x; });
+          return "([0-9]+)";
+        }
+        // TODO %I: hour (12-hour clock) [1,12]
+        // TODO %j: day number [1,366]
+        case '%m': {
+          fields.push(function(x) { month = x - 1; });
+          return "([0-9]+)";
+        }
+        case '%M': {
+          fields.push(function(x) { minute = x; });
+          return "([0-9]+)";
+        }
+        // TODO %n: any white space
+        // TODO %p: locale's equivalent of a.m. or p.m.
+        // TODO %r: %I:%M:%S %p
+        // TODO %R: %H:%M
+        case '%S': {
+          fields.push(function(x) { second = x; });
+          return "([0-9]+)";
+        }
+        // TODO %t: any white space
+        // TODO %T: %H:%M:%S
+        // TODO %U: week number [00,53]
+        // TODO %w: weekday [0,6]
+        // TODO %W: week number [00, 53]
+        // TODO %x: locale date (%m/%d/%y)
+        // TODO %X: locale time (%I:%M:%S %p)
+        case '%y': {
+          fields.push(function(x) {
+              x = Number(x);
+              year = x + (((0 <= x) && (x < 69)) ? 2000
+                  : (((x >= 69) && (x < 100) ? 1900 : 0)));
+            });
+          return "([0-9]+)";
+        }
+        case '%Y': {
+          fields.push(function(x) { year = x; });
+          return "([0-9]+)";
+        }
+        case '%%': {
+          fields.push(function() {});
+          return "%";
+        }
+      }
+      return s;
+    });
+
+  var match = s.match(format);
+  if (match) match.forEach(function(m, i) { fields[i](m); });
+  return new Date(year, month, date, hour, minute, second);
+};
+
+if (Date.prototype.toLocaleFormat) {
+  Date.prototype.format = Date.prototype.toLocaleFormat;
+} else {
+
+/**
+ * Converts a date to a string using the specified formatting. If the
+ * <tt>Date</tt> object already supports the <tt>toLocaleFormat</tt> method, as
+ * in Firefox, this is simply an alias to the built-in method.
+ *
+ * <p>The format string is in the same format expected by the <tt>strftime</tt>
+ * function in C. The following conversion specifications are supported:<ul>
+ *
+ * <li>%a - abbreviated weekday name.</li>
+ * <li>%A - full weekday name.</li>
+ * <li>%b - abbreviated month names.</li>
+ * <li>%B - full month names.</li>
+ * <li>%c - locale's appropriate date and time.</li>
+ * <li>%C - century number.</li>
+ * <li>%d - day of month [01,31] (zero padded).</li>
+ * <li>%D - same as %m/%d/%y.</li>
+ * <li>%e - day of month [ 1,31] (space padded).</li>
+ * <li>%h - same as %b.</li>
+ * <li>%H - hour (24-hour clock) [00,23] (zero padded).</li>
+ * <li>%I - hour (12-hour clock) [01,12] (zero padded).</li>
+ * <li>%m - month number [01,12] (zero padded).</li>
+ * <li>%M - minute [0,59] (zero padded).</li>
+ * <li>%n - newline character.</li>
+ * <li>%p - locale's equivalent of a.m. or p.m.</li>
+ * <li>%r - same as %I:%M:%S %p.</li>
+ * <li>%R - same as %H:%M.</li>
+ * <li>%S - second [00,61] (zero padded).</li>
+ * <li>%t - tab character.</li>
+ * <li>%T - same as %H:%M:%S.</li>
+ * <li>%x - same as %m/%d/%y.</li>
+ * <li>%X - same as %I:%M:%S %p.</li>
+ * <li>%y - year with century [00,99] (zero padded).</li>
+ * <li>%Y - year including century.</li>
+ * <li>%% - %.</li>
+ *
+ * </ul>The following conversion specifications are <i>unsupported</i> (for now):<ul>
+ *
+ * <li>%j - day number [1,366].</li>
+ * <li>%u - weekday number [1,7].</li>
+ * <li>%U - week number [00,53].</li>
+ * <li>%V - week number [01,53].</li>
+ * <li>%w - weekday number [0,6].</li>
+ * <li>%W - week number [00,53].</li>
+ * <li>%Z - timezone name or abbreviation.</li>
+ *
+ * </ul>
+ *
+ * @see <a
+ * href="http://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Date/toLocaleFormat">Date.toLocaleFormat</a>
+ * documentation.
+ * @see <a
+ * href="http://www.opengroup.org/onlinepubs/007908799/xsh/strftime.html">strftime</a>
+ * documentation.
+ * @param {string} format a format string.
+ * @returns {string} the formatted date.
+ */
+Date.prototype.format = function(format) {
+  function pad(n, p) { return (n < 10) ? (p || "0") + n : n; }
+  var d = this;
+  return format.replace(/%[a-zA-Z0-9]/g, function(s) {
+      switch (s) {
+        case '%a': return [
+            "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
+          ][d.getDay()];
+        case '%A': return [
+            "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday",
+            "Saturday"
+          ][d.getDay()];
+        case '%h':
+        case '%b': return [
+            "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep",
+            "Oct", "Nov", "Dec"
+          ][d.getMonth()];
+        case '%B': return [
+            "January", "February", "March", "April", "May", "June", "July",
+            "August", "September", "October", "November", "December"
+          ][d.getMonth()];
+        case '%c': return d.toLocaleString();
+        case '%C': return pad(Math.floor(d.getFullYear() / 100) % 100);
+        case '%d': return pad(d.getDate());
+        case '%x':
+        case '%D': return pad(d.getMonth() + 1)
+                  + "/" + pad(d.getDate())
+                  + "/" + pad(d.getFullYear() % 100);
+        case '%e': return pad(d.getDate(), " ");
+        case '%H': return pad(d.getHours());
+        case '%I': {
+          var h = d.getHours() % 12;
+          return h ? pad(h) : 12;
+        }
+        // TODO %j: day of year as a decimal number [001,366]
+        case '%m': return pad(d.getMonth() + 1);
+        case '%M': return pad(d.getMinutes());
+        case '%n': return "\n";
+        case '%p': return d.getHours() < 12 ? "AM" : "PM";
+        case '%T':
+        case '%X':
+        case '%r': {
+          var h = d.getHours() % 12;
+          return (h ? pad(h) : 12)
+                  + ":" + pad(d.getMinutes())
+                  + ":" + pad(d.getSeconds())
+                  + " " + (d.getHours() < 12 ? "AM" : "PM");
+        }
+        case '%R': return pad(d.getHours()) + ":" + pad(d.getMinutes());
+        case '%S': return pad(d.getSeconds());
+        case '%t': return "\t";
+        case '%u': {
+          var w = d.getDay();
+          return w ? w : 1;
+        }
+        // TODO %U: week number (sunday first day) [00,53]
+        // TODO %V: week number (monday first day) [01,53] ... with weirdness
+        case '%w': return d.getDay();
+        // TODO %W: week number (monday first day) [00,53] ... with weirdness
+        case '%y': return pad(d.getFullYear() % 100);
+        case '%Y': return d.getFullYear();
+        // TODO %Z: timezone name or abbreviation
+        case '%%': return "%";
+      }
+      return s;
+    });
+  };
+}
+var pv = function() {/**
+ * The top-level Protovis namespace. All public methods and fields should be
+ * registered on this object. Note that core Protovis source is surrounded by an
+ * anonymous function, so any other declared globals will not be visible outside
+ * of core methods. This also allows multiple versions of Protovis to coexist,
+ * since each version will see their own <tt>pv</tt> namespace.
+ *
+ * @namespace The top-level Protovis namespace, <tt>pv</tt>.
+ */
+var pv = {};
+
+/**
+ * @private Returns a prototype object suitable for extending the given class
+ * <tt>f</tt>. Rather than constructing a new instance of <tt>f</tt> to serve as
+ * the prototype (which unnecessarily runs the constructor on the created
+ * prototype object, potentially polluting it), an anonymous function is
+ * generated internally that shares the same prototype:
+ *
+ * <pre>function g() {}
+ * g.prototype = f.prototype;
+ * return new g();</pre>
+ *
+ * For more details, see Douglas Crockford's essay on prototypal inheritance.
+ *
+ * @param {function} f a constructor.
+ * @returns a suitable prototype object.
+ * @see Douglas Crockford's essay on <a
+ * href="http://javascript.crockford.com/prototypal.html">prototypal
+ * inheritance</a>.
+ */
+pv.extend = function(f) {
+  function g() {}
+  g.prototype = f.prototype || f;
+  return new g();
+};
+
+try {
+  eval("pv.parse = function(x) x;"); // native support
+} catch (e) {
+
+/**
+ * @private Parses a Protovis specification, which may use JavaScript 1.8
+ * function expresses, replacing those function expressions with proper
+ * functions such that the code can be run by a JavaScript 1.6 interpreter. This
+ * hack only supports function expressions (using clumsy regular expressions, no
+ * less), and not other JavaScript 1.8 features such as let expressions.
+ *
+ * @param {string} s a Protovis specification (i.e., a string of JavaScript 1.8
+ * source code).
+ * @returns {string} a conformant JavaScript 1.6 source code.
+ */
+  pv.parse = function(js) { // hacky regex support
+    var re = new RegExp("function(\\s+\\w+)?\\([^)]*\\)\\s*", "mg"), m, d, i = 0, s = "";
+    while (m = re.exec(js)) {
+      var j = m.index + m[0].length;
+      if (js.charAt(j--) != '{') {
+        s += js.substring(i, j) + "{return ";
+        i = j;
+        for (var p = 0; p >= 0 && j < js.length; j++) {
+          var c = js.charAt(j);
+          switch (c) {
+            case '"': case '\'': {
+              while (++j < js.length && (d = js.charAt(j)) != c) {
+                if (d == '\\') j++;
+              }
+              break;
+            }
+            case '[': case '(': p++; break;
+            case ']': case ')': p--; break;
+            case ';':
+            case ',': if (p == 0) p--; break;
+          }
+        }
+        s += pv.parse(js.substring(i, --j)) + ";}";
+        i = j;
+      }
+      re.lastIndex = j;
+    }
+    s += js.substring(i);
+    return s;
+  };
+}
+
+/**
+ * Returns the passed-in argument, <tt>x</tt>; the identity function. This method
+ * is provided for convenience since it is used as the default behavior for a
+ * number of property functions.
+ *
+ * @param x a value.
+ * @returns the value <tt>x</tt>.
+ */
+pv.identity = function(x) { return x; };
+
+/**
+ * Returns <tt>this.index</tt>. This method is provided for convenience for use
+ * with scales. For example, to color bars by their index, say:
+ *
+ * <pre>.fillStyle(pv.Colors.category10().by(pv.index))</pre>
+ *
+ * This method is equivalent to <tt>function() this.index</tt>, but more
+ * succinct. Note that the <tt>index</tt> property is also supported for
+ * accessor functions with {@link pv.max}, {@link pv.min} and other array
+ * utility methods.
+ *
+ * @see pv.Scale
+ * @see pv.Mark#index
+ */
+pv.index = function() { return this.index; };
+
+/**
+ * Returns <tt>this.childIndex</tt>. This method is provided for convenience for
+ * use with scales. For example, to color bars by their child index, say:
+ *
+ * <pre>.fillStyle(pv.Colors.category10().by(pv.child))</pre>
+ *
+ * This method is equivalent to <tt>function() this.childIndex</tt>, but more
+ * succinct.
+ *
+ * @see pv.Scale
+ * @see pv.Mark#childIndex
+ */
+pv.child = function() { return this.childIndex; };
+
+/**
+ * Returns <tt>this.parent.index</tt>. This method is provided for convenience
+ * for use with scales. This method is provided for convenience for use with
+ * scales. For example, to color bars by their parent index, say:
+ *
+ * <pre>.fillStyle(pv.Colors.category10().by(pv.parent))</pre>
+ *
+ * Tthis method is equivalent to <tt>function() this.parent.index</tt>, but more
+ * succinct.
+ *
+ * @see pv.Scale
+ * @see pv.Mark#index
+ */
+pv.parent = function() { return this.parent.index; };
+
+/**
+ * Returns an array of numbers, starting at <tt>start</tt>, incrementing by
+ * <tt>step</tt>, until <tt>stop</tt> is reached. The stop value is exclusive. If
+ * only a single argument is specified, this value is interpeted as the
+ * <i>stop</i> value, with the <i>start</i> value as zero. If only two arguments
+ * are specified, the step value is implied to be one.
+ *
+ * <p>The method is modeled after the built-in <tt>range</tt> method from
+ * Python. See the Python documentation for more details.
+ *
+ * @see <a href="http://docs.python.org/library/functions.html#range">Python range</a>
+ * @param {number} [start] the start value.
+ * @param {number} stop the stop value.
+ * @param {number} [step] the step value.
+ * @returns {number[]} an array of numbers.
+ */
+pv.range = function(start, stop, step) {
+  if (arguments.length == 1) {
+    stop = start;
+    start = 0;
+  }
+  if (step == undefined) step = 1;
+  else if (!step) throw new Error("step must be non-zero");
+  var array = [], i = 0, j;
+  if (step < 0) {
+    while ((j = start + step * i++) > stop) {
+      array.push(j);
+    }
+  } else {
+    while ((j = start + step * i++) < stop) {
+      array.push(j);
+    }
+  }
+  return array;
+};
+
+/**
+ * Returns a random number in the range [<tt>min</tt>, <tt>max</tt>) that is a
+ * multiple of <tt>step</tt>. More specifically, the returned number is of the
+ * form <tt>min</tt> + <i>n</i> * <tt>step</tt>, where <i>n</i> is a nonnegative
+ * integer. If <tt>step</tt> is not specified, it defaults to 1, returning a
+ * random integer if <tt>min</tt> is also an integer.
+ *
+ * @param min {number} minimum value.
+ * @param [max] {number} maximum value.
+ * @param [step] {numbeR} step value.
+ */
+pv.random = function(min, max, step) {
+  if (arguments.length == 1) {
+    max = min;
+    min = 0;
+  }
+  if (step == undefined) {
+    step = 1;
+  }
+  return step
+      ? (Math.floor(Math.random() * (max - min) / step) * step + min)
+      : (Math.random() * (max - min) + min);
+};
+
+/**
+ * Concatenates the specified array with itself <i>n</i> times. For example,
+ * <tt>pv.repeat([1, 2])</tt> returns [1, 2, 1, 2].
+ *
+ * @param {array} a an array.
+ * @param {number} [n] the number of times to repeat; defaults to two.
+ * @returns {array} an array that repeats the specified array.
+ */
+pv.repeat = function(array, n) {
+  if (arguments.length == 1) n = 2;
+  return pv.blend(pv.range(n).map(function() { return array; }));
+};
+
+/**
+ * Given two arrays <tt>a</tt> and <tt>b</tt>, <style
+ * type="text/css">sub{line-height:0}</style> returns an array of all possible
+ * pairs of elements [a<sub>i</sub>, b<sub>j</sub>]. The outer loop is on array
+ * <i>a</i>, while the inner loop is on <i>b</i>, such that the order of
+ * returned elements is [a<sub>0</sub>, b<sub>0</sub>], [a<sub>0</sub>,
+ * b<sub>1</sub>], ... [a<sub>0</sub>, b<sub>m</sub>], [a<sub>1</sub>,
+ * b<sub>0</sub>], [a<sub>1</sub>, b<sub>1</sub>], ... [a<sub>1</sub>,
+ * b<sub>m</sub>], ... [a<sub>n</sub>, b<sub>m</sub>]. If either array is empty,
+ * an empty array is returned.
+ *
+ * @param {array} a an array.
+ * @param {array} b an array.
+ * @returns {array} an array of pairs of elements in <tt>a</tt> and <tt>b</tt>.
+ */
+pv.cross = function(a, b) {
+  var array = [];
+  for (var i = 0, n = a.length, m = b.length; i < n; i++) {
+    for (var j = 0, x = a[i]; j < m; j++) {
+      array.push([x, b[j]]);
+    }
+  }
+  return array;
+};
+
+/**
+ * Given the specified array of arrays, concatenates the arrays into a single
+ * array. If the individual arrays are explicitly known, an alternative to blend
+ * is to use JavaScript's <tt>concat</tt> method directly. These two equivalent
+ * expressions:<ul>
+ *
+ * <li><tt>pv.blend([[1, 2, 3], ["a", "b", "c"]])</tt>
+ * <li><tt>[1, 2, 3].concat(["a", "b", "c"])</tt>
+ *
+ * </ul>return [1, 2, 3, "a", "b", "c"].
+ *
+ * @param {array[]} arrays an array of arrays.
+ * @returns {array} an array containing all the elements of each array in
+ * <tt>arrays</tt>.
+ */
+pv.blend = function(arrays) {
+  return Array.prototype.concat.apply([], arrays);
+};
+
+/**
+ * Given the specified array of arrays, <style
+ * type="text/css">sub{line-height:0}</style> transposes each element
+ * array<sub>ij</sub> with array<sub>ji</sub>. If the array has dimensions
+ * <i>n</i>&times;<i>m</i>, it will have dimensions <i>m</i>&times;<i>n</i>
+ * after this method returns. This method transposes the elements of the array
+ * in place, mutating the array, and returning a reference to the array.
+ *
+ * @param {array[]} arrays an array of arrays.
+ * @returns {array[]} the passed-in array, after transposing the elements.
+ */
+pv.transpose = function(arrays) {
+  var n = arrays.length, m = pv.max(arrays, function(d) { return d.length; });
+
+  if (m > n) {
+    arrays.length = m;
+    for (var i = n; i < m; i++) {
+      arrays[i] = new Array(n);
+    }
+    for (var i = 0; i < n; i++) {
+      for (var j = i + 1; j < m; j++) {
+        var t = arrays[i][j];
+        arrays[i][j] = arrays[j][i];
+        arrays[j][i] = t;
+      }
+    }
+  } else {
+    for (var i = 0; i < m; i++) {
+      arrays[i].length = n;
+    }
+    for (var i = 0; i < n; i++) {
+      for (var j = 0; j < i; j++) {
+        var t = arrays[i][j];
+        arrays[i][j] = arrays[j][i];
+        arrays[j][i] = t;
+      }
+    }
+  }
+
+  arrays.length = m;
+  for (var i = 0; i < m; i++) {
+    arrays[i].length = n;
+  }
+
+  return arrays;
+};
+
+/**
+ * Returns all of the property names (keys) of the specified object (a map). The
+ * order of the returned array is not defined.
+ *
+ * @param map an object.
+ * @returns {string[]} an array of strings corresponding to the keys.
+ * @see #entries
+ */
+pv.keys = function(map) {
+  var array = [];
+  for (var key in map) {
+    array.push(key);
+  }
+  return array;
+};
+
+/**
+ * Returns all of the entries (key-value pairs) of the specified object (a
+ * map). The order of the returned array is not defined. Each key-value pair is
+ * represented as an object with <tt>key</tt> and <tt>value</tt> attributes,
+ * e.g., <tt>{key: "foo", value: 42}</tt>.
+ *
+ * @param map an object.
+ * @returns {array} an array of key-value pairs corresponding to the keys.
+ */
+pv.entries = function(map) {
+  var array = [];
+  for (var key in map) {
+    array.push({ key: key, value: map[key] });
+  }
+  return array;
+};
+
+/**
+ * Returns all of the values (attribute values) of the specified object (a
+ * map). The order of the returned array is not defined.
+ *
+ * @param map an object.
+ * @returns {array} an array of objects corresponding to the values.
+ * @see #entries
+ */
+pv.values = function(map) {
+  var array = [];
+  for (var key in map) {
+    array.push(map[key]);
+  }
+  return array;
+};
+
+/**
+ * @private A private variant of Array.prototype.map that supports the index
+ * property.
+ */
+function map(array, f) {
+  var o = {};
+  return f
+      ? array.map(function(d, i) { o.index = i; return f.call(o, d); })
+      : array.slice();
+};
+
+/**
+ * Returns a normalized copy of the specified array, such that the sum of the
+ * returned elements sum to one. If the specified array is not an array of
+ * numbers, an optional accessor function <tt>f</tt> can be specified to map the
+ * elements to numbers. For example, if <tt>array</tt> is an array of objects,
+ * and each object has a numeric property "foo", the expression
+ *
+ * <pre>pv.normalize(array, function(d) d.foo)</pre>
+ *
+ * returns a normalized array on the "foo" property. If an accessor function is
+ * not specified, the identity function is used. Accessor functions can refer to
+ * <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number[]} an array of numbers that sums to one.
+ */
+pv.normalize = function(array, f) {
+  var norm = map(array, f), sum = pv.sum(norm);
+  for (var i = 0; i < norm.length; i++) norm[i] /= sum;
+  return norm;
+};
+
+/**
+ * Returns the sum of the specified array. If the specified array is not an
+ * array of numbers, an optional accessor function <tt>f</tt> can be specified
+ * to map the elements to numbers. See {@link #normalize} for an example.
+ * Accessor functions can refer to <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number} the sum of the specified array.
+ */
+pv.sum = function(array, f) {
+  var o = {};
+  return array.reduce(f
+      ? function(p, d, i) { o.index = i; return p + f.call(o, d); }
+      : function(p, d) { return p + d; }, 0);
+};
+
+/**
+ * Returns the maximum value of the specified array. If the specified array is
+ * not an array of numbers, an optional accessor function <tt>f</tt> can be
+ * specified to map the elements to numbers. See {@link #normalize} for an
+ * example. Accessor functions can refer to <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number} the maximum value of the specified array.
+ */
+pv.max = function(array, f) {
+  if (f == pv.index) return array.length - 1;
+  return Math.max.apply(null, f ? map(array, f) : array);
+};
+
+/**
+ * Returns the index of the maximum value of the specified array. If the
+ * specified array is not an array of numbers, an optional accessor function
+ * <tt>f</tt> can be specified to map the elements to numbers. See
+ * {@link #normalize} for an example. Accessor functions can refer to
+ * <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number} the index of the maximum value of the specified array.
+ */
+pv.max.index = function(array, f) {
+  if (f == pv.index) return array.length - 1;
+  if (!f) f = pv.identity;
+  var maxi = -1, maxx = -Infinity, o = {};
+  for (var i = 0; i < array.length; i++) {
+    o.index = i;
+    var x = f.call(o, array[i]);
+    if (x > maxx) {
+      maxx = x;
+      maxi = i;
+    }
+  }
+  return maxi;
+}
+
+/**
+ * Returns the minimum value of the specified array of numbers. If the specified
+ * array is not an array of numbers, an optional accessor function <tt>f</tt>
+ * can be specified to map the elements to numbers. See {@link #normalize} for
+ * an example. Accessor functions can refer to <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number} the minimum value of the specified array.
+ */
+pv.min = function(array, f) {
+  if (f == pv.index) return 0;
+  return Math.min.apply(null, f ? map(array, f) : array);
+};
+
+/**
+ * Returns the index of the minimum value of the specified array. If the
+ * specified array is not an array of numbers, an optional accessor function
+ * <tt>f</tt> can be specified to map the elements to numbers. See
+ * {@link #normalize} for an example. Accessor functions can refer to
+ * <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number} the index of the minimum value of the specified array.
+ */
+pv.min.index = function(array, f) {
+  if (f == pv.index) return 0;
+  if (!f) f = pv.identity;
+  var mini = -1, minx = Infinity, o = {};
+  for (var i = 0; i < array.length; i++) {
+    o.index = i;
+    var x = f.call(o, array[i]);
+    if (x < minx) {
+      minx = x;
+      mini = i;
+    }
+  }
+  return mini;
+}
+
+/**
+ * Returns the arithmetic mean, or average, of the specified array. If the
+ * specified array is not an array of numbers, an optional accessor function
+ * <tt>f</tt> can be specified to map the elements to numbers. See
+ * {@link #normalize} for an example. Accessor functions can refer to
+ * <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number} the mean of the specified array.
+ */
+pv.mean = function(array, f) {
+  return pv.sum(array, f) / array.length;
+};
+
+/**
+ * Returns the median of the specified array. If the specified array is not an
+ * array of numbers, an optional accessor function <tt>f</tt> can be specified
+ * to map the elements to numbers. See {@link #normalize} for an example.
+ * Accessor functions can refer to <tt>this.index</tt>.
+ *
+ * @param {array} array an array of objects, or numbers.
+ * @param {function} [f] an optional accessor function.
+ * @returns {number} the median of the specified array.
+ */
+pv.median = function(array, f) {
+  if (f == pv.index) return (array.length - 1) / 2;
+  array = map(array, f).sort(pv.naturalOrder);
+  if (array.length % 2) return array[Math.floor(array.length / 2)];
+  var i = array.length / 2;
+  return (array[i - 1] + array[i]) / 2;
+};
+
+/**
+ * Returns a map constructed from the specified <tt>keys</tt>, using the
+ * function <tt>f</tt> to compute the value for each key. The single argument to
+ * the value function is the key. The callback is invoked only for indexes of
+ * the array which have assigned values; it is not invoked for indexes which
+ * have been deleted or which have never been assigned values.
+ *
+ * <p>For example, this expression creates a map from strings to string length:
+ *
+ * <pre>pv.dict(["one", "three", "seventeen"], function(s) s.length)</pre>
+ *
+ * The returned value is <tt>{one: 3, three: 5, seventeen: 9}</tt>. Accessor
+ * functions can refer to <tt>this.index</tt>.
+ *
+ * @param {array} keys an array.
+ * @param {function} f a value function.
+ * @returns a map from keys to values.
+ */
+pv.dict = function(keys, f) {
+  var m = {}, o = {};
+  for (var i = 0; i < keys.length; i++) {
+    if (i in keys) {
+      var k = keys[i];
+      o.index = i;
+      m[k] = f.call(o, k);
+    }
+  }
+  return m;
+};
+
+/**
+ * Returns a permutation of the specified array, using the specified array of
+ * indexes. The returned array contains the corresponding element in
+ * <tt>array</tt> for each index in <tt>indexes</tt>, in order. For example,
+ *
+ * <pre>pv.permute(["a", "b", "c"], [1, 2, 0])</pre>
+ *
+ * returns <tt>["b", "c", "a"]</tt>. It is acceptable for the array of indexes
+ * to be a different length from the array of elements, and for indexes to be
+ * duplicated or omitted. The optional accessor function <tt>f</tt> can be used
+ * to perform a simultaneous mapping of the array elements. Accessor functions
+ * can refer to <tt>this.index</tt>.
+ *
+ * @param {array} array an array.
+ * @param {number[]} indexes an array of indexes into <tt>array</tt>.
+ * @param {function} [f] an optional accessor function.
+ * @returns {array} an array of elements from <tt>array</tt>; a permutation.
+ */
+pv.permute = function(array, indexes, f) {
+  if (!f) f = pv.identity;
+  var p = new Array(indexes.length), o = {};
+  indexes.forEach(function(j, i) { o.index = j; p[i] = f.call(o, array[j]); });
+  return p;
+};
+
+/**
+ * Returns a map from key to index for the specified <tt>keys</tt> array. For
+ * example,
+ *
+ * <pre>pv.numerate(["a", "b", "c"])</pre>
+ *
+ * returns <tt>{a: 0, b: 1, c: 2}</tt>. Note that since JavaScript maps only
+ * support string keys, <tt>keys</tt> must contain strings, or other values that
+ * naturally map to distinct string values. Alternatively, an optional accessor
+ * function <tt>f</tt> can be specified to compute the string key for the given
+ * element. Accessor functions can refer to <tt>this.index</tt>.
+ *
+ * @param {array} keys an array, usually of string keys.
+ * @param {function} [f] an optional key function.
+ * @returns a map from key to index.
+ */
+pv.numerate = function(keys, f) {
+  if (!f) f = pv.identity;
+  var map = {}, o = {};
+  keys.forEach(function(x, i) { o.index = i; map[f.call(o, x)] = i; });
+  return map;
+};
+
+/**
+ * The comparator function for natural order. This can be used in conjunction with
+ * the built-in array <tt>sort</tt> method to sort elements by their natural
+ * order, ascending. Note that if no comparator function is specified to the
+ * built-in <tt>sort</tt> method, the default order is lexicographic, <i>not</i>
+ * natural!
+ *
+ * @see <a
+ * href="http://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Array/sort">Array.sort</a>.
+ * @param a an element to compare.
+ * @param b an element to compare.
+ * @returns {number} negative if a &lt; b; positive if a &gt; b; otherwise 0.
+ */
+pv.naturalOrder = function(a, b) {
+  return (a < b) ? -1 : ((a > b) ? 1 : 0);
+};
+
+/**
+ * The comparator function for reverse natural order. This can be used in
+ * conjunction with the built-in array <tt>sort</tt> method to sort elements by
+ * their natural order, descending. Note that if no comparator function is
+ * specified to the built-in <tt>sort</tt> method, the default order is
+ * lexicographic, <i>not</i> natural!
+ *
+ * @see #naturalOrder
+ * @param a an element to compare.
+ * @param b an element to compare.
+ * @returns {number} negative if a &lt; b; positive if a &gt; b; otherwise 0.
+ */
+pv.reverseOrder = function(b, a) {
+  return (a < b) ? -1 : ((a > b) ? 1 : 0);
+};
+
+/**
+ * @private Computes the value of the specified CSS property <tt>p</tt> on the
+ * specified element <tt>e</tt>.
+ *
+ * @param {string} p the name of the CSS property.
+ * @param e the element on which to compute the CSS property.
+ */
+pv.css = function(e, p) {
+  return window.getComputedStyle
+      ? window.getComputedStyle(e, null).getPropertyValue(p)
+      : e.currentStyle[p];
+};
+
+/**
+ * Namespace constants for SVG, XMLNS, and XLINK.
+ *
+ * @namespace Namespace constants for SVG, XMLNS, and XLINK.
+ */
+pv.ns = {
+  /**
+   * The SVG namespace, "http://www.w3.org/2000/svg".
+   *
+   * @type string
+   * @constant
+   */
+  svg: "http://www.w3.org/2000/svg",
+
+  /**
+   * The XMLNS namespace, "http://www.w3.org/2000/xmlns".
+   *
+   * @type string
+   * @constant
+   */
+  xmlns: "http://www.w3.org/2000/xmlns",
+
+  /**
+   * The XLINK namespace, "http://www.w3.org/1999/xlink".
+   *
+   * @type string
+   * @constant
+   */
+  xlink: "http://www.w3.org/1999/xlink"
+};
+
+/**
+ * Protovis major and minor version numbers.
+ *
+ * @namespace Protovis major and minor version numbers.
+ */
+pv.version = {
+  /**
+   * The major version number.
+   *
+   * @type number
+   * @constant
+   */
+  major: 3,
+
+  /**
+   * The minor version number.
+   *
+   * @type number
+   * @constant
+   */
+  minor: 1
+};
+
+/**
+ * @private Reports the specified error to the JavaScript console. Mozilla only
+ * allows logging to the console for privileged code; if the console is
+ * unavailable, the alert dialog box is used instead.
+ *
+ * @param e the exception that triggered the error.
+ */
+pv.error = function(e) {
+  (typeof console == "undefined") ? alert(e) : console.error(e);
+};
+
+/**
+ * @private Registers the specified listener for events of the specified type on
+ * the specified target. For standards-compliant browsers, this method uses
+ * <tt>addEventListener</tt>; for Internet Explorer, <tt>attachEvent</tt>.
+ *
+ * @param target a DOM element.
+ * @param {string} type the type of event, such as "click".
+ * @param {function} the listener callback function.
+ */
+pv.listen = function(target, type, listener) {
+  return target.addEventListener
+    ? target.addEventListener(type, listener, false)
+    : target.attachEvent("on" + type, listener);
+};
+
+/**
+ * Returns the logarithm with a given base value.
+ *
+ * @param {number} x the number for which to compute the logarithm.
+ * @param {number} b the base of the logarithm.
+ * @returns {number} the logarithm value.
+ */
+pv.log = function(x, b) {
+  return Math.log(x) / Math.log(b);
+};
+
+/**
+ * Computes a zero-symmetric logarithm. Computes the logarithm of the absolute
+ * value of the input, and determines the sign of the output according to the
+ * sign of the input value.
+ *
+ * @param {number} x the number for which to compute the logarithm.
+ * @param {number} b the base of the logarithm.
+ * @returns {number} the symmetric log value.
+ */
+pv.logSymmetric = function(x, b) {
+  return (x == 0) ? 0 : ((x < 0) ? -pv.log(-x, b) : pv.log(x, b));
+};
+
+/**
+ * Computes a zero-symmetric logarithm, with adjustment to values between zero
+ * and the logarithm base. This adjustment introduces distortion for values less
+ * than the base number, but enables simultaneous plotting of log-transformed
+ * data involving both positive and negative numbers.
+ *
+ * @param {number} x the number for which to compute the logarithm.
+ * @param {number} b the base of the logarithm.
+ * @returns {number} the adjusted, symmetric log value.
+ */
+pv.logAdjusted = function(x, b) {
+  var negative = x < 0;
+  if (x < b) x += (b - x) / b;
+  return negative ? -pv.log(x, b) : pv.log(x, b);
+};
+
+/**
+ * Rounds an input value down according to its logarithm. The method takes the
+ * floor of the logarithm of the value and then uses the resulting value as an
+ * exponent for the base value.
+ *
+ * @param {number} x the number for which to compute the logarithm floor.
+ * @param {number} b the base of the logarithm.
+ * @return {number} the rounded-by-logarithm value.
+ */
+pv.logFloor = function(x, b) {
+  return (x > 0)
+      ? Math.pow(b, Math.floor(pv.log(x, b)))
+      : -Math.pow(b, -Math.floor(-pv.log(-x, b)));
+};
+
+/**
+ * Rounds an input value up according to its logarithm. The method takes the
+ * ceiling of the logarithm of the value and then uses the resulting value as an
+ * exponent for the base value.
+ *
+ * @param {number} x the number for which to compute the logarithm ceiling.
+ * @param {number} b the base of the logarithm.
+ * @return {number} the rounded-by-logarithm value.
+ */
+pv.logCeil = function(x, b) {
+  return (x > 0)
+      ? Math.pow(b, Math.ceil(pv.log(x, b)))
+      : -Math.pow(b, -Math.ceil(-pv.log(-x, b)));
+};
+
+/**
+ * Searches the specified array of numbers for the specified value using the
+ * binary search algorithm. The array must be sorted (as by the <tt>sort</tt>
+ * method) prior to making this call. If it is not sorted, the results are
+ * undefined. If the array contains multiple elements with the specified value,
+ * there is no guarantee which one will be found.
+ *
+ * <p>The <i>insertion point</i> is defined as the point at which the value
+ * would be inserted into the array: the index of the first element greater than
+ * the value, or <tt>array.length</tt>, if all elements in the array are less
+ * than the specified value. Note that this guarantees that the return value
+ * will be nonnegative if and only if the value is found.
+ *
+ * @param {number[]} array the array to be searched.
+ * @param {number} value the value to be searched for.
+ * @returns the index of the search value, if it is contained in the array;
+ * otherwise, (-(<i>insertion point</i>) - 1).
+ * @param {function} [f] an optional key function.
+ */
+pv.search = function(array, value, f) {
+  if (!f) f = pv.identity;
+  var low = 0, high = array.length - 1;
+  while (low <= high) {
+    var mid = (low + high) >> 1, midValue = f(array[mid]);
+    if (midValue < value) low = mid + 1;
+    else if (midValue > value) high = mid - 1;
+    else return mid;
+  }
+  return -low - 1;
+};
+
+pv.search.index = function(array, value, f) {
+  var i = pv.search(array, value, f);
+  return (i < 0) ? (-i - 1) : i;
+};
+/**
+ * Returns a {@link pv.Tree} operator for the specified array. This is a
+ * convenience factory method, equivalent to <tt>new pv.Tree(array)</tt>.
+ *
+ * @see pv.Tree
+ * @param {array} array an array from which to construct a tree.
+ * @returns {pv.Tree} a tree operator for the specified array.
+ */
+pv.tree = function(array) {
+  return new pv.Tree(array);
+};
+
+/**
+ * Constructs a tree operator for the specified array. This constructor should
+ * not be invoked directly; use {@link pv.tree} instead.
+ *
+ * @class Represents a tree operator for the specified array. The tree operator
+ * allows a hierarchical map to be constructed from an array; it is similar to
+ * the {@link pv.Nest} operator, except the hierarchy is derived dynamically
+ * from the array elements.
+ *
+ * <p>For example, given an array of size information for ActionScript classes:
+ *
+ * <pre>{ name: "flare.flex.FlareVis", size: 4116 },
+ * { name: "flare.physics.DragForce", size: 1082 },
+ * { name: "flare.physics.GravityForce", size: 1336 }, ...</pre>
+ *
+ * To facilitate visualization, it may be useful to nest the elements by their
+ * package hierarchy:
+ *
+ * <pre>var tree = pv.tree(classes)
+ *     .keys(function(d) d.name.split("."))
+ *     .map();</pre>
+ *
+ * The resulting tree is:
+ *
+ * <pre>{ flare: {
+ *     flex: {
+ *       FlareVis: {
+ *         name: "flare.flex.FlareVis",
+ *         size: 4116 } },
+ *     physics: {
+ *       DragForce: {
+ *         name: "flare.physics.DragForce",
+ *         size: 1082 },
+ *       GravityForce: {
+ *         name: "flare.physics.GravityForce",
+ *         size: 1336 } },
+ *     ... } }</pre>
+ *
+ * By specifying a value function,
+ *
+ * <pre>var tree = pv.tree(classes)
+ *     .keys(function(d) d.name.split("."))
+ *     .value(function(d) d.size)
+ *     .map();</pre>
+ *
+ * we can further eliminate redundant data:
+ *
+ * <pre>{ flare: {
+ *     flex: {
+ *       FlareVis: 4116 },
+ *     physics: {
+ *       DragForce: 1082,
+ *       GravityForce: 1336 },
+ *   ... } }</pre>
+ *
+ * For visualizations with large data sets, performance improvements may be seen
+ * by storing the data in a tree format, and then flattening it into an array at
+ * runtime with {@link pv.Flatten}.
+ *
+ * @param {array} array an array from which to construct a tree.
+ */
+pv.Tree = function(array) {
+  this.array = array;
+};
+
+/**
+ * Assigns a <i>keys</i> function to this operator; required. The keys function
+ * returns an array of <tt>string</tt>s for each element in the associated
+ * array; these keys determine how the elements are nested in the tree. The
+ * returned keys should be unique for each element in the array; otherwise, the
+ * behavior of this operator is undefined.
+ *
+ * @param {function} k the keys function.
+ * @returns {pv.Tree} this.
+ */
+pv.Tree.prototype.keys = function(k) {
+  this.k = k;
+  return this;
+};
+
+/**
+ * Assigns a <i>value</i> function to this operator; optional. The value
+ * function specifies an optional transformation of the element in the array
+ * before it is inserted into the map. If no value function is specified, it is
+ * equivalent to using the identity function.
+ *
+ * @param {function} k the value function.
+ * @returns {pv.Tree} this.
+ */
+pv.Tree.prototype.value = function(v) {
+  this.v = v;
+  return this;
+};
+
+/**
+ * Returns a hierarchical map of values. The hierarchy is determined by the keys
+ * function; the values in the map are determined by the value function.
+ *
+ * @returns a hierarchical map of values.
+ */
+pv.Tree.prototype.map = function() {
+  var map = {}, o = {};
+  for (var i = 0; i < this.array.length; i++) {
+    o.index = i;
+    var value = this.array[i], keys = this.k.call(o, value), node = map;
+    for (var j = 0; j < keys.length - 1; j++) {
+      node = node[keys[j]] || (node[keys[j]] = {});
+    }
+    node[keys[j]] = this.v ? this.v.call(o, value) : value;
+  }
+  return map;
+};
+/**
+ * Returns a {@link pv.Nest} operator for the specified array. This is a
+ * convenience factory method, equivalent to <tt>new pv.Nest(array)</tt>.
+ *
+ * @see pv.Nest
+ * @param {array} array an array of elements to nest.
+ * @returns {pv.Nest} a nest operator for the specified array.
+ */
+pv.nest = function(array) {
+  return new pv.Nest(array);
+};
+
+/**
+ * Constructs a nest operator for the specified array. This constructor should
+ * not be invoked directly; use {@link pv.nest} instead.
+ *
+ * @class Represents a {@link Nest} operator for the specified array. Nesting
+ * allows elements in an array to be grouped into a hierarchical tree
+ * structure. The levels in the tree are specified by <i>key</i> functions. The
+ * leaf nodes of the tree can be sorted by value, while the internal nodes can
+ * be sorted by key. Finally, the tree can be returned either has a
+ * multidimensional array via {@link #entries}, or as a hierarchical map via
+ * {@link #map}. The {@link #rollup} routine similarly returns a map, collapsing
+ * the elements in each leaf node using a summary function.
+ *
+ * <p>For example, consider the following tabular data structure of Barley
+ * yields, from various sites in Minnesota during 1931-2:
+ *
+ * <pre>{ yield: 27.00, variety: "Manchuria", year: 1931, site: "University Farm" },
+ * { yield: 48.87, variety: "Manchuria", year: 1931, site: "Waseca" },
+ * { yield: 27.43, variety: "Manchuria", year: 1931, site: "Morris" }, ...</pre>
+ *
+ * To facilitate visualization, it may be useful to nest the elements first by
+ * year, and then by variety, as follows:
+ *
+ * <pre>var nest = pv.nest(yields)
+ *     .key(function(d) d.year)
+ *     .key(function(d) d.variety)
+ *     .entries();</pre>
+ *
+ * This returns a nested array. Each element of the outer array is a key-values
+ * pair, listing the values for each distinct key:
+ *
+ * <pre>{ key: 1931, values: [
+ *   { key: "Manchuria", values: [
+ *       { yield: 27.00, variety: "Manchuria", year: 1931, site: "University Farm" },
+ *       { yield: 48.87, variety: "Manchuria", year: 1931, site: "Waseca" },
+ *       { yield: 27.43, variety: "Manchuria", year: 1931, site: "Morris" },
+ *       ...
+ *     ] },
+ *   { key: "Glabron", values: [
+ *       { yield: 43.07, variety: "Glabron", year: 1931, site: "University Farm" },
+ *       { yield: 55.20, variety: "Glabron", year: 1931, site: "Waseca" },
+ *       ...
+ *     ] },
+ *   ] },
+ * { key: 1932, values: ... }</pre>
+ *
+ * Further details, including sorting and rollup, is provided below on the
+ * corresponding methods.
+ *
+ * @param {array} array an array of elements to nest.
+ */
+pv.Nest = function(array) {
+  this.array = array;
+  this.keys = [];
+};
+
+/**
+ * Nests using the specified key function. Multiple keys may be added to the
+ * nest; the array elements will be nested in the order keys are specified.
+ *
+ * @param {function} key a key function; must return a string or suitable map
+ * key.
+ * @return {pv.Nest} this.
+ */
+pv.Nest.prototype.key = function(key) {
+  this.keys.push(key);
+  return this;
+};
+
+/**
+ * Sorts the previously-added keys. The natural sort order is used by default
+ * (see {@link pv.naturalOrder}); if an alternative order is desired,
+ * <tt>order</tt> should be a comparator function. If this method is not called
+ * (i.e., keys are <i>unsorted</i>), keys will appear in the order they appear
+ * in the underlying elements array. For example,
+ *
+ * <pre>pv.nest(yields)
+ *     .key(function(d) d.year)
+ *     .key(function(d) d.variety)
+ *     .sortKeys()
+ *     .entries()</pre>
+ *
+ * groups yield data by year, then variety, and sorts the variety groups
+ * lexicographically (since the variety attribute is a string).
+ *
+ * <p>Key sort order is only used in conjunction with {@link #entries}, which
+ * returns an array of key-values pairs. If the nest is used to construct a
+ * {@link #map} instead, keys are unsorted.
+ *
+ * @param {function} [order] an optional comparator function.
+ * @returns {pv.Nest} this.
+ */
+pv.Nest.prototype.sortKeys = function(order) {
+  this.keys[this.keys.length - 1].order = order || pv.naturalOrder;
+  return this;
+};
+
+/**
+ * Sorts the leaf values. The natural sort order is used by default (see
+ * {@link pv.naturalOrder}); if an alternative order is desired, <tt>order</tt>
+ * should be a comparator function. If this method is not called (i.e., values
+ * are <i>unsorted</i>), values will appear in the order they appear in the
+ * underlying elements array. For example,
+ *
+ * <pre>pv.nest(yields)
+ *     .key(function(d) d.year)
+ *     .key(function(d) d.variety)
+ *     .sortValues(function(a, b) a.yield - b.yield)
+ *     .entries()</pre>
+ *
+ * groups yield data by year, then variety, and sorts the values for each
+ * variety group by yield.
+ *
+ * <p>Value sort order, unlike keys, applies to both {@link #entries} and
+ * {@link #map}. It has no effect on {@link #rollup}.
+ *
+ * @param {function} [order] an optional comparator function.
+ * @return {pv.Nest} this.
+ */
+pv.Nest.prototype.sortValues = function(order) {
+  this.order = order || pv.naturalOrder;
+  return this;
+};
+
+/**
+ * Returns a hierarchical map of values. Each key adds one level to the
+ * hierarchy. With only a single key, the returned map will have a key for each
+ * distinct value of the key function; the correspond value with be an array of
+ * elements with that key value. If a second key is added, this will be a nested
+ * map. For example:
+ *
+ * <pre>pv.nest(yields)
+ *     .key(function(d) d.variety)
+ *     .key(function(d) d.site)
+ *     .map()</pre>
+ *
+ * returns a map <tt>m</tt> such that <tt>m[variety][site]</tt> is an array, a subset of
+ * <tt>yields</tt>, with each element having the given variety and site.
+ *
+ * @returns a hierarchical map of values.
+ */
+pv.Nest.prototype.map = function() {
+  var map = {}, values = [];
+
+  /* Build the map. */
+  for (var i, j = 0; j < this.array.length; j++) {
+    var x = this.array[j];
+    var m = map;
+    for (i = 0; i < this.keys.length - 1; i++) {
+      var k = this.keys[i](x);
+      if (!m[k]) m[k] = {};
+      m = m[k];
+    }
+    k = this.keys[i](x);
+    if (!m[k]) {
+      var a = [];
+      values.push(a);
+      m[k] = a;
+    }
+    m[k].push(x);
+  }
+
+  /* Sort each leaf array. */
+  if (this.order) {
+    for (var i = 0; i < values.length; i++) {
+      values[i].sort(this.order);
+    }
+  }
+
+  return map;
+};
+
+/**
+ * Returns a hierarchical nested array. This method is similar to
+ * {@link pv.entries}, but works recursively on the entire hierarchy. Rather
+ * than returning a map like {@link #map}, this method returns a nested
+ * array. Each element of the array has a <tt>key</tt> and <tt>values</tt>
+ * field. For leaf nodes, the <tt>values</tt> array will be a subset of the
+ * underlying elements array; for non-leaf nodes, the <tt>values</tt> array will
+ * contain more key-values pairs.
+ *
+ * <p>For an example usage, see the {@link Nest} constructor.
+ *
+ * @returns a hierarchical nested array.
+ */
+pv.Nest.prototype.entries = function() {
+
+  /** Recursively extracts the entries for the given map. */
+  function entries(map) {
+    var array = [];
+    for (var k in map) {
+      var v = map[k];
+      array.push({ key: k, values: (v instanceof Array) ? v : entries(v) });
+    };
+    return array;
+  }
+
+  /** Recursively sorts the values for the given key-values array. */
+  function sort(array, i) {
+    var o = this.keys[i].order;
+    if (o) array.sort(function(a, b) { return o(a.key, b.key); });
+    if (++i < this.keys.length) {
+      for (var j = 0; j < array.length; j++) {
+        sort.call(this, array[j].values, i);
+      }
+    }
+    return array;
+  }
+
+  return sort.call(this, entries(this.map()), 0);
+};
+
+/**
+ * Returns a rollup map. The behavior of this method is the same as
+ * {@link #map}, except that the leaf values are replaced with the return value
+ * of the specified rollup function <tt>f</tt>. For example,
+ *
+ * <pre>pv.nest(yields)
+ *      .key(function(d) d.site)
+ *      .rollup(function(v) pv.median(v, function(d) d.yield))</pre>
+ *
+ * first groups yield data by site, and then returns a map from site to median
+ * yield for the given site.
+ *
+ * @see #map
+ * @param {function} f a rollup function.
+ * @returns a hierarchical map, with the leaf values computed by <tt>f</tt>.
+ */
+pv.Nest.prototype.rollup = function(f) {
+
+  /** Recursively descends to the leaf nodes (arrays) and does rollup. */
+  function rollup(map) {
+    for (var key in map) {
+      var value = map[key];
+      if (value instanceof Array) {
+        map[key] = f(value);
+      } else {
+        rollup(value);
+      }
+    }
+    return map;
+  }
+
+  return rollup(this.map());
+};
+/**
+ * Returns a {@link pv.Flatten} operator for the specified map. This is a
+ * convenience factory method, equivalent to <tt>new pv.Flatten(map)</tt>.
+ *
+ * @see pv.Flatten
+ * @param map a map to flatten.
+ * @returns {pv.Flatten} a flatten operator for the specified map.
+ */
+pv.flatten = function(map) {
+  return new pv.Flatten(map);
+};
+
+/**
+ * Constructs a flatten operator for the specified map. This constructor should
+ * not be invoked directly; use {@link pv.flatten} instead.
+ *
+ * @class Represents a flatten operator for the specified array. Flattening
+ * allows hierarchical maps to be flattened into an array. The levels in the
+ * input tree are specified by <i>key</i> functions.
+ *
+ * <p>For example, consider the following hierarchical data structure of Barley
+ * yields, from various sites in Minnesota during 1931-2:
+ *
+ * <pre>{ 1931: {
+ *     Manchuria: {
+ *       "University Farm": 27.00,
+ *       "Waseca": 48.87,
+ *       "Morris": 27.43,
+ *       ... },
+ *     Glabron: {
+ *       "University Farm": 43.07,
+ *       "Waseca": 55.20,
+ *       ... } },
+ *   1932: {
+ *     ... } }</pre>
+ *
+ * To facilitate visualization, it may be useful to flatten the tree into a
+ * tabular array:
+ *
+ * <pre>var array = pv.flatten(yields)
+ *     .key("year")
+ *     .key("variety")
+ *     .key("site")
+ *     .key("yield")
+ *     .array();</pre>
+ *
+ * This returns an array of object elements. Each element in the array has
+ * attributes corresponding to this flatten operator's keys:
+ *
+ * <pre>{ site: "University Farm", variety: "Manchuria", year: 1931, yield: 27 },
+ * { site: "Waseca", variety: "Manchuria", year: 1931, yield: 48.87 },
+ * { site: "Morris", variety: "Manchuria", year: 1931, yield: 27.43 },
+ * { site: "University Farm", variety: "Glabron", year: 1931, yield: 43.07 },
+ * { site: "Waseca", variety: "Glabron", year: 1931, yield: 55.2 }, ...</pre>
+ *
+ * <p>The flatten operator is roughly the inverse of the {@link pv.Nest} and
+ * {@link pv.Tree} operators.
+ *
+ * @param map a map to flatten.
+ */
+pv.Flatten = function(map) {
+  this.map = map;
+  this.keys = [];
+};
+
+/**
+ * Flattens using the specified key function. Multiple keys may be added to the
+ * flatten; the tiers of the underlying tree must correspond to the specified
+ * keys, in order. The order of the returned array is undefined; however, you
+ * can easily sort it.
+ *
+ * @param {string} key the key name.
+ * @param {function} [f] an optional value map function.
+ * @return {pv.Nest} this.
+ */
+pv.Flatten.prototype.key = function(key, f) {
+  this.keys.push({name: key, value: f});
+  return this;
+};
+
+/**
+ * Returns the flattened array. Each entry in the array is an object; each
+ * object has attributes corresponding to this flatten operator's keys.
+ *
+ * @returns an array of elements from the flattened map.
+ */
+pv.Flatten.prototype.array = function() {
+  var entries = [], stack = [], keys = this.keys;
+
+  /* Recursively visits the specified value. */
+  function visit(value, i) {
+    if (i < keys.length - 1) {
+      for (var key in value) {
+        stack.push(key);
+        visit(value[key], i + 1);
+        stack.pop();
+      }
+    } else {
+      entries.push(stack.concat(value));
+    }
+  }
+
+  visit(this.map, 0);
+  return entries.map(function(stack) {
+      var m = {};
+      for (var i = 0; i < keys.length; i++) {
+        var k = keys[i], v = stack[i];
+        m[k.name] = k.value ? k.value.call(null, v) : v;
+      }
+      return m;
+    });
+};
+/**
+ * Returns a {@link pv.Vector} for the specified <i>x</i> and <i>y</i>
+ * coordinate. This is a convenience factory method, equivalent to <tt>new
+ * pv.Vector(x, y)</tt>.
+ *
+ * @see pv.Vector
+ * @param {number} x the <i>x</i> coordinate.
+ * @param {number} y the <i>y</i> coordinate.
+ * @returns {pv.Vector} a vector for the specified coordinates.
+ */
+pv.vector = function(x, y) {
+  return new pv.Vector(x, y);
+};
+
+/**
+ * Constructs a {@link pv.Vector} for the specified <i>x</i> and <i>y</i>
+ * coordinate. This constructor should not be invoked directly; use
+ * {@link pv.vector} instead.
+ *
+ * @class Represents a two-dimensional vector; a 2-tuple <i>&#x27e8;x,
+ * y&#x27e9;</i>.
+ *
+ * @param {number} x the <i>x</i> coordinate.
+ * @param {number} y the <i>y</i> coordinate.
+ */
+pv.Vector = function(x, y) {
+  this.x = x;
+  this.y = y;
+};
+
+/**
+ * Returns a vector perpendicular to this vector: <i>&#x27e8;-y, x&#x27e9;</i>.
+ *
+ * @returns {pv.Vector} a perpendicular vector.
+ */
+pv.Vector.prototype.perp = function() {
+  return new pv.Vector(-this.y, this.x);
+};
+
+/**
+ * Returns a normalized copy of this vector: a vector with the same direction,
+ * but unit length. If this vector has zero length this method returns a copy of
+ * this vector.
+ *
+ * @returns {pv.Vector} a unit vector.
+ */
+pv.Vector.prototype.norm = function() {
+  var l = this.length();
+  return this.times(l ? (1 / l) : 1);
+};
+
+/**
+ * Returns the magnitude of this vector, defined as <i>sqrt(x * x + y * y)</i>.
+ *
+ * @returns {number} a length.
+ */
+pv.Vector.prototype.length = function() {
+  return Math.sqrt(this.x * this.x + this.y * this.y);
+};
+
+/**
+ * Returns a scaled copy of this vector: <i>&#x27e8;x * k, y * k&#x27e9;</i>.
+ * To perform the equivalent divide operation, use <i>1 / k</i>.
+ *
+ * @param {number} k the scale factor.
+ * @returns {pv.Vector} a scaled vector.
+ */
+pv.Vector.prototype.times = function(k) {
+  return new pv.Vector(this.x * k, this.y * k);
+};
+
+/**
+ * Returns this vector plus the vector <i>v</i>: <i>&#x27e8;x + v.x, y +
+ * v.y&#x27e9;</i>. If only one argument is specified, it is interpreted as the
+ * vector <i>v</i>.
+ *
+ * @param {number} x the <i>x</i> coordinate to add.
+ * @param {number} y the <i>y</i> coordinate to add.
+ * @returns {pv.Vector} a new vector.
+ */
+pv.Vector.prototype.plus = function(x, y) {
+  return (arguments.length == 1)
+      ? new pv.Vector(this.x + x.x, this.y + x.y)
+      : new pv.Vector(this.x + x, this.y + y);
+};
+
+/**
+ * Returns this vector minus the vector <i>v</i>: <i>&#x27e8;x - v.x, y -
+ * v.y&#x27e9;</i>. If only one argument is specified, it is interpreted as the
+ * vector <i>v</i>.
+ *
+ * @param {number} x the <i>x</i> coordinate to subtract.
+ * @param {number} y the <i>y</i> coordinate to subtract.
+ * @returns {pv.Vector} a new vector.
+ */
+pv.Vector.prototype.minus = function(x, y) {
+  return (arguments.length == 1)
+      ? new pv.Vector(this.x - x.x, this.y - x.y)
+      : new pv.Vector(this.x - x, this.y - y);
+};
+
+/**
+ * Returns the dot product of this vector and the vector <i>v</i>: <i>x * v.x +
+ * y * v.y</i>. If only one argument is specified, it is interpreted as the
+ * vector <i>v</i>.
+ *
+ * @param {number} x the <i>x</i> coordinate to dot.
+ * @param {number} y the <i>y</i> coordinate to dot.
+ * @returns {number} a dot product.
+ */
+pv.Vector.prototype.dot = function(x, y) {
+  return (arguments.length == 1)
+      ? this.x * x.x + this.y * x.y
+      : this.x * x + this.y * y;
+};
+// TODO code-sharing between scales
+
+/**
+ * @ignore
+ * @class
+ */
+pv.Scale = function() {};
+
+/**
+ * @private Returns a function that interpolators from the start value to the
+ * end value, given a parameter <i>t</i> in [0, 1].
+ *
+ * @param start the start value.
+ * @param end the end value.
+ */
+pv.Scale.interpolator = function(start, end) {
+  if (typeof start == "number") {
+    return function(t) {
+      return t * (end - start) + start;
+    };
+  }
+
+  /* For now, assume color. */
+  start = pv.color(start).rgb();
+  end = pv.color(end).rgb();
+  return function(t) {
+    var a = start.a * (1 - t) + end.a * t;
+    if (a < 1e-5) a = 0; // avoid scientific notation
+    return (start.a == 0) ? pv.rgb(end.r, end.g, end.b, a)
+        : ((end.a == 0) ? pv.rgb(start.r, start.g, start.b, a)
+        : pv.rgb(
+            Math.round(start.r * (1 - t) + end.r * t),
+            Math.round(start.g * (1 - t) + end.g * t),
+            Math.round(start.b * (1 - t) + end.b * t), a));
+  };
+};
+/**
+ * Returns a linear scale for the specified domain. The arguments to this
+ * constructor are optional, and equivalent to calling {@link #domain}.
+ *
+ * @class Represents a linear scale. <style
+ * type="text/css">sub{line-height:0}</style> <img src="../linear.png"
+ * width="180" height="175" align="right"> Most commonly, a linear scale
+ * represents a 1-dimensional linear transformation from a numeric domain of
+ * input data [<i>d<sub>0</sub></i>, <i>d<sub>1</sub></i>] to a numeric range of
+ * pixels [<i>r<sub>0</sub></i>, <i>r<sub>1</sub></i>]. The equation for such a
+ * scale is:
+ *
+ * <blockquote><i>f(x) = (x - d<sub>0</sub>) / (d<sub>1</sub> - d<sub>0</sub>) *
+ * (r<sub>1</sub> - r<sub>0</sub>) + r<sub>0</sub></i></blockquote>
+ *
+ * For example, a linear scale from the domain [0, 100] to range [0, 640]:
+ *
+ * <blockquote><i>f(x) = (x - 0) / (100 - 0) * (640 - 0) + 0</i><br>
+ * <i>f(x) = x / 100 * 640</i><br>
+ * <i>f(x) = x * 6.4</i><br>
+ * </blockquote>
+ *
+ * Thus, saying
+ *
+ * <pre>.height(function(d) d * 6.4)</pre>
+ *
+ * is identical to
+ *
+ * <pre>.height(pv.Scale.linear(0, 100).range(0, 640))</pre>
+ *
+ * As you can see, scales do not always make code smaller, but they should make
+ * code more explicit and easier to maintain. In addition to readability, scales
+ * offer several useful features:
+ *
+ * <p>1. The range can be expressed in colors, rather than pixels. Changing the
+ * example above to
+ *
+ * <pre>.fillStyle(pv.Scale.linear(0, 100).range("red", "green"))</pre>
+ *
+ * will cause it to fill the marks "red" on an input value of 0, "green" on an
+ * input value of 100, and some color in-between for intermediate values.
+ *
+ * <p>2. The domain and range can be subdivided for a "poly-linear"
+ * transformation. For example, you may want a diverging color scale that is
+ * increasingly red for negative values, and increasingly green for positive
+ * values:
+ *
+ * <pre>.fillStyle(pv.Scale.linear(-1, 0, 1).range("red", "white", "green"))</pre>
+ *
+ * The domain can be specified as a series of <i>n</i> monotonically-increasing
+ * values; the range must also be specified as <i>n</i> values, resulting in
+ * <i>n - 1</i> contiguous linear scales.
+ *
+ * <p>3. Linear scales can be inverted for interaction. The {@link #invert}
+ * method takes a value in the output range, and returns the corresponding value
+ * in the input domain. This is frequently used to convert the mouse location
+ * (see {@link pv.Mark#mouse}) to a value in the input domain. Note that
+ * inversion is only supported for numeric ranges, and not colors.
+ *
+ * <p>4. A scale can be queried for reasonable "tick" values. The {@link #ticks}
+ * method provides a convenient way to get a series of evenly-spaced rounded
+ * values in the input domain. Frequently these are used in conjunction with
+ * {@link pv.Rule} to display tick marks or grid lines.
+ *
+ * <p>5. A scale can be "niced" to extend the domain to suitable rounded
+ * numbers. If the minimum and maximum of the domain are messy because they are
+ * derived from data, you can use {@link #nice} to round these values down and
+ * up to even numbers.
+ *
+ * @param {number...} domain... domain values.
+ * @returns {pv.Scale.linear} a linear scale.
+ */
+pv.Scale.linear = function() {
+  var d = [0, 1], r = [0, 1], i = [pv.identity], precision = 0;
+
+  /** @private */
+  function scale(x) {
+    var j = pv.search(d, x);
+    if (j < 0) j = -j - 2;
+    j = Math.max(0, Math.min(i.length - 1, j));
+    return i[j]((x - d[j]) / (d[j + 1] - d[j]));
+  }
+
+  /**
+   * Sets or gets the input domain. This method can be invoked several ways:
+   *
+   * <p>1. <tt>domain(min, ..., max)</tt>
+   *
+   * <p>Specifying the domain as a series of numbers is the most explicit and
+   * recommended approach. Most commonly, two numbers are specified: the minimum
+   * and maximum value. However, for a diverging scale, or other subdivided
+   * poly-linear scales, multiple values can be specified. Values can be derived
+   * from data using {@link pv.min} and {@link pv.max}. For example:
+   *
+   * <pre>.domain(0, pv.max(array))</pre>
+   *
+   * An alternative method for deriving minimum and maximum values from data
+   * follows.
+   *
+   * <p>2. <tt>domain(array, minf, maxf)</tt>
+   *
+   * <p>When both the minimum and maximum value are derived from data, the
+   * arguments to the <tt>domain</tt> method can be specified as the array of
+   * data, followed by zero, one or two accessor functions. For example, if the
+   * array of data is just an array of numbers:
+   *
+   * <pre>.domain(array)</pre>
+   *
+   * On the other hand, if the array elements are objects representing stock
+   * values per day, and the domain should consider the stock's daily low and
+   * daily high:
+   *
+   * <pre>.domain(array, function(d) d.low, function(d) d.high)</pre>
+   *
+   * The first method of setting the domain is preferred because it is more
+   * explicit; setting the domain using this second method should be used only
+   * if brevity is required.
+   *
+   * <p>3. <tt>domain()</tt>
+   *
+   * <p>Invoking the <tt>domain</tt> method with no arguments returns the
+   * current domain as an array of numbers.
+   *
+   * @function
+   * @name pv.Scale.linear.prototype.domain
+   * @param {number...} domain... domain values.
+   * @returns {pv.Scale.linear} <tt>this</tt>, or the current domain.
+   */
+  scale.domain = function(array, min, max) {
+    if (arguments.length) {
+      if (array instanceof Array) {
+        if (arguments.length < 2) min = pv.identity;
+        if (arguments.length < 3) max = min;
+        d = [pv.min(array, min), pv.max(array, max)];
+      } else {
+        d = Array.prototype.slice.call(arguments);
+      }
+      return this;
+    }
+    return d;
+  };
+
+  /**
+   * Sets or gets the output range. This method can be invoked several ways:
+   *
+   * <p>1. <tt>range(min, ..., max)</tt>
+   *
+   * <p>The range may be specified as a series of numbers or colors. Most
+   * commonly, two numbers are specified: the minimum and maximum pixel values.
+   * For a color scale, values may be specified as {@link pv.Color}s or
+   * equivalent strings. For a diverging scale, or other subdivided poly-linear
+   * scales, multiple values can be specified. For example:
+   *
+   * <pre>.range("red", "white", "green")</pre>
+   *
+   * <p>Currently, only numbers and colors are supported as range values. The
+   * number of range values must exactly match the number of domain values, or
+   * the behavior of the scale is undefined.
+   *
+   * <p>2. <tt>range()</tt>
+   *
+   * <p>Invoking the <tt>range</tt> method with no arguments returns the current
+   * range as an array of numbers or colors.
+   *
+   * @function
+   * @name pv.Scale.linear.prototype.range
+   * @param {...} range... range values.
+   * @returns {pv.Scale.linear} <tt>this</tt>, or the current range.
+   */
+  scale.range = function() {
+    if (arguments.length) {
+      r = Array.prototype.slice.call(arguments);
+      i = [];
+      for (var j = 0; j < r.length - 1; j++) {
+        i.push(pv.Scale.interpolator(r[j], r[j + 1]));
+      }
+      return this;
+    }
+    return r;
+  };
+
+  /**
+   * Inverts the specified value in the output range, returning the
+   * corresponding value in the input domain. This is frequently used to convert
+   * the mouse location (see {@link pv.Mark#mouse}) to a value in the input
+   * domain. Inversion is only supported for numeric ranges, and not colors.
+   *
+   * <p>Note that this method does not do any rounding or bounds checking. If
+   * the input domain is discrete (e.g., an array index), the returned value
+   * should be rounded. If the specified <tt>y</tt> value is outside the range,
+   * the returned value may be equivalently outside the input domain.
+   *
+   * @function
+   * @name pv.Scale.linear.prototype.invert
+   * @param {number} y a value in the output range (a pixel location).
+   * @returns {number} a value in the input domain.
+   */
+  scale.invert = function(y) {
+    var j = pv.search(r, y);
+    if (j < 0) j = -j - 2;
+    j = Math.max(0, Math.min(i.length - 1, j));
+    return (y - r[j]) / (r[j + 1] - r[j]) * (d[j + 1] - d[j]) + d[j];
+  };
+
+  /**
+   * Returns an array of evenly-spaced, suitably-rounded values in the input
+   * domain. This method attempts to return between 5 and 10 tick values. These
+   * values are frequently used in conjunction with {@link pv.Rule} to display
+   * tick marks or grid lines.
+   *
+   * @function
+   * @name pv.Scale.linear.prototype.ticks
+   * @returns {number[]} an array input domain values to use as ticks.
+   */
+  scale.ticks = function() {
+    var min = d[0],
+        max = d[d.length - 1],
+        span = max - min,
+        step = pv.logCeil(span / 10, 10);
+    if (span / step < 2) step /= 5;
+    else if (span / step < 5) step /= 2;
+    var start = Math.ceil(min / step) * step,
+        end = Math.floor(max / step) * step;
+    precision = Math.max(0, -Math.floor(pv.log(step, 10) + .01));
+    return pv.range(start, end + step, step);
+  };
+
+  /**
+   * Formats the specified tick value using the appropriate precision, based on
+   * the step interval between tick marks.
+   *
+   * @function
+   * @name pv.Scale.linear.prototype.tickFormat
+   * @param {number} t a tick value.
+   * @return {string} a formatted tick value.
+   */
+  scale.tickFormat = function(t) {
+    return t.toFixed(precision);
+  };
+
+  /**
+   * "Nices" this scale, extending the bounds of the input domain to
+   * evenly-rounded values. Nicing is useful if the domain is computed
+   * dynamically from data, and may be irregular. For example, given a domain of
+   * [0.20147987687960267, 0.996679553296417], a call to <tt>nice()</tt> might
+   * extend the domain to [0.2, 1].
+   *
+   * <p>This method must be invoked each time after setting the domain.
+   *
+   * @function
+   * @name pv.Scale.linear.prototype.nice
+   * @returns {pv.Scale.linear} <tt>this</tt>.
+   */
+  scale.nice = function() {
+    var min = d[0],
+        max = d[d.length - 1],
+        step = Math.pow(10, Math.round(Math.log(max - min) / Math.log(10)) - 1);
+    d = [Math.floor(min / step) * step, Math.ceil(max / step) * step];
+    return this;
+  };
+
+  /**
+   * Returns a view of this scale by the specified accessor function <tt>f</tt>.
+   * Given a scale <tt>y</tt>, <tt>y.by(function(d) d.foo)</tt> is equivalent to
+   * <tt>function(d) y(d.foo)</tt>.
+   *
+   * <p>This method is provided for convenience, such that scales can be
+   * succinctly defined inline. For example, given an array of data elements
+   * that have a <tt>score</tt> attribute with the domain [0, 1], the height
+   * property could be specified as:
+   *
+   * <pre>.height(pv.Scale.linear().range(0, 480).by(function(d) d.score))</pre>
+   *
+   * This is equivalent to:
+   *
+   * <pre>.height(function(d) d.score * 480)</pre>
+   *
+   * This method should be used judiciously; it is typically more clear to
+   * invoke the scale directly, passing in the value to be scaled.
+   *
+   * @function
+   * @name pv.Scale.linear.prototype.by
+   * @param {function} f an accessor function.
+   * @returns {pv.Scale.linear} a view of this scale by the specified accessor
+   * function.
+   */
+  scale.by = function(f) {
+    function by() { return scale(f.apply(this, arguments)); }
+    for (var method in scale) by[method] = scale[method];
+    return by;
+  };
+
+  scale.domain.apply(scale, arguments);
+  return scale;
+};
+/**
+ * Returns a log scale for the specified domain. The arguments to this
+ * constructor are optional, and equivalent to calling {@link #domain}.
+ *
+ * @class Represents a log scale. <style
+ * type="text/css">sub{line-height:0}</style> <img src="../log.png"
+ * width="190" height="175" align="right"> Most commonly, a log scale represents
+ * a 1-dimensional log transformation from a numeric domain of input data
+ * [<i>d<sub>0</sub></i>, <i>d<sub>1</sub></i>] to a numeric range of pixels
+ * [<i>r<sub>0</sub></i>, <i>r<sub>1</sub></i>]. The equation for such a scale
+ * is:
+ *
+ * <blockquote><i>f(x) = (log(x) - log(d<sub>0</sub>)) / (log(d<sub>1</sub>) -
+ * log(d<sub>0</sub>)) * (r<sub>1</sub> - r<sub>0</sub>) +
+ * r<sub>0</sub></i></blockquote>
+ *
+ * where <i>log(x)</i> represents the zero-symmetric logarthim of <i>x</i> using
+ * the scale's associated base (default: 10, see {@link pv.logSymmetric}). For
+ * example, a log scale from the domain [1, 100] to range [0, 640]:
+ *
+ * <blockquote><i>f(x) = (log(x) - log(1)) / (log(100) - log(1)) * (640 - 0) + 0</i><br>
+ * <i>f(x) = log(x) / 2 * 640</i><br>
+ * <i>f(x) = log(x) * 320</i><br>
+ * </blockquote>
+ *
+ * Thus, saying
+ *
+ * <pre>.height(function(d) Math.log(d) * 138.974)</pre>
+ *
+ * is equivalent to
+ *
+ * <pre>.height(pv.Scale.log(1, 100).range(0, 640))</pre>
+ *
+ * As you can see, scales do not always make code smaller, but they should make
+ * code more explicit and easier to maintain. In addition to readability, scales
+ * offer several useful features:
+ *
+ * <p>1. The range can be expressed in colors, rather than pixels. Changing the
+ * example above to
+ *
+ * <pre>.fillStyle(pv.Scale.log(1, 100).range("red", "green"))</pre>
+ *
+ * will cause it to fill the marks "red" on an input value of 1, "green" on an
+ * input value of 100, and some color in-between for intermediate values.
+ *
+ * <p>2. The domain and range can be subdivided for a "poly-log"
+ * transformation. For example, you may want a diverging color scale that is
+ * increasingly red for small values, and increasingly green for large values:
+ *
+ * <pre>.fillStyle(pv.Scale.log(1, 10, 100).range("red", "white", "green"))</pre>
+ *
+ * The domain can be specified as a series of <i>n</i> monotonically-increasing
+ * values; the range must also be specified as <i>n</i> values, resulting in
+ * <i>n - 1</i> contiguous log scales.
+ *
+ * <p>3. Log scales can be inverted for interaction. The {@link #invert} method
+ * takes a value in the output range, and returns the corresponding value in the
+ * input domain. This is frequently used to convert the mouse location (see
+ * {@link pv.Mark#mouse}) to a value in the input domain. Note that inversion is
+ * only supported for numeric ranges, and not colors.
+ *
+ * <p>4. A scale can be queried for reasonable "tick" values. The {@link #ticks}
+ * method provides a convenient way to get a series of evenly-spaced rounded
+ * values in the input domain. Frequently these are used in conjunction with
+ * {@link pv.Rule} to display tick marks or grid lines.
+ *
+ * <p>5. A scale can be "niced" to extend the domain to suitable rounded
+ * numbers. If the minimum and maximum of the domain are messy because they are
+ * derived from data, you can use {@link #nice} to round these values down and
+ * up to even numbers.
+ *
+ * @param {number...} domain... domain values.
+ * @returns {pv.Scale.log} a log scale.
+ */
+pv.Scale.log = function() {
+  var d = [1, 10], l = [0, 1], b = 10, r = [0, 1], i = [pv.identity];
+
+  /** @private */
+  function scale(x) {
+    var j = pv.search(d, x);
+    if (j < 0) j = -j - 2;
+    j = Math.max(0, Math.min(i.length - 1, j));
+    return i[j]((log(x) - l[j]) / (l[j + 1] - l[j]));
+  }
+
+  /** @private */
+  function log(x) {
+    return pv.logSymmetric(x, b);
+  }
+
+  /**
+   * Sets or gets the input domain. This method can be invoked several ways:
+   *
+   * <p>1. <tt>domain(min, ..., max)</tt>
+   *
+   * <p>Specifying the domain as a series of numbers is the most explicit and
+   * recommended approach. Most commonly, two numbers are specified: the minimum
+   * and maximum value. However, for a diverging scale, or other subdivided
+   * poly-log scales, multiple values can be specified. Values can be derived
+   * from data using {@link pv.min} and {@link pv.max}. For example:
+   *
+   * <pre>.domain(1, pv.max(array))</pre>
+   *
+   * An alternative method for deriving minimum and maximum values from data
+   * follows.
+   *
+   * <p>2. <tt>domain(array, minf, maxf)</tt>
+   *
+   * <p>When both the minimum and maximum value are derived from data, the
+   * arguments to the <tt>domain</tt> method can be specified as the array of
+   * data, followed by zero, one or two accessor functions. For example, if the
+   * array of data is just an array of numbers:
+   *
+   * <pre>.domain(array)</pre>
+   *
+   * On the other hand, if the array elements are objects representing stock
+   * values per day, and the domain should consider the stock's daily low and
+   * daily high:
+   *
+   * <pre>.domain(array, function(d) d.low, function(d) d.high)</pre>
+   *
+   * The first method of setting the domain is preferred because it is more
+   * explicit; setting the domain using this second method should be used only
+   * if brevity is required.
+   *
+   * <p>3. <tt>domain()</tt>
+   *
+   * <p>Invoking the <tt>domain</tt> method with no arguments returns the
+   * current domain as an array of numbers.
+   *
+   * @function
+   * @name pv.Scale.log.prototype.domain
+   * @param {number...} domain... domain values.
+   * @returns {pv.Scale.log} <tt>this</tt>, or the current domain.
+   */
+  scale.domain = function(array, min, max) {
+    if (arguments.length) {
+      if (array instanceof Array) {
+        if (arguments.length < 2) min = pv.identity;
+        if (arguments.length < 3) max = min;
+        d = [pv.min(array, min), pv.max(array, max)];
+      } else {
+        d = Array.prototype.slice.call(arguments);
+      }
+      l = d.map(log);
+      return this;
+    }
+    return d;
+  };
+
+  /**
+   * @function
+   * @name pv.Scale.log.prototype.range
+   * @param {...} range... range values.
+   * @returns {pv.Scale.log} <tt>this</tt>.
+   */
+  scale.range = function() {
+    if (arguments.length) {
+      r = Array.prototype.slice.call(arguments);
+      i = [];
+      for (var j = 0; j < r.length - 1; j++) {
+        i.push(pv.Scale.interpolator(r[j], r[j + 1]));
+      }
+      return this;
+    }
+    return r;
+  };
+
+  /**
+   * Sets or gets the output range. This method can be invoked several ways:
+   *
+   * <p>1. <tt>range(min, ..., max)</tt>
+   *
+   * <p>The range may be specified as a series of numbers or colors. Most
+   * commonly, two numbers are specified: the minimum and maximum pixel values.
+   * For a color scale, values may be specified as {@link pv.Color}s or
+   * equivalent strings. For a diverging scale, or other subdivided poly-log
+   * scales, multiple values can be specified. For example:
+   *
+   * <pre>.range("red", "white", "green")</pre>
+   *
+   * <p>Currently, only numbers and colors are supported as range values. The
+   * number of range values must exactly match the number of domain values, or
+   * the behavior of the scale is undefined.
+   *
+   * <p>2. <tt>range()</tt>
+   *
+   * <p>Invoking the <tt>range</tt> method with no arguments returns the current
+   * range as an array of numbers or colors.
+   *
+   * @function
+   * @name pv.Scale.log.prototype.invert
+   * @param {...} range... range values.
+   * @returns {pv.Scale.log} <tt>this</tt>, or the current range.
+   */
+  scale.invert = function(y) {
+    var j = pv.search(r, y);
+    if (j < 0) j = -j - 2;
+    j = Math.max(0, Math.min(i.length - 1, j));
+    var t = l[j] + (y - r[j]) / (r[j + 1] - r[j]) * (l[j + 1] - l[j]);
+    return (d[j] < 0) ? -Math.pow(b, -t) : Math.pow(b, t);
+  };
+
+  /**
+   * Returns an array of evenly-spaced, suitably-rounded values in the input
+   * domain. These values are frequently used in conjunction with {@link
+   * pv.Rule} to display tick marks or grid lines.
+   *
+   * @function
+   * @name pv.Scale.log.prototype.ticks
+   * @returns {number[]} an array input domain values to use as ticks.
+   */
+  scale.ticks = function() {
+    // TODO: support multiple domains
+    var start = Math.floor(l[0]),
+        end = Math.ceil(l[1]),
+        ticks = [];
+    for (var i = start; i < end; i++) {
+      var x = Math.pow(b, i);
+      if (d[0] < 0) x = -x;
+      for (var j = 1; j < b; j++) {
+        ticks.push(x * j);
+      }
+    }
+    ticks.push(Math.pow(b, end));
+    if (ticks[0] < d[0]) ticks.shift();
+    if (ticks[ticks.length - 1] > d[1]) ticks.pop();
+    return ticks;
+  };
+
+  /**
+   * Formats the specified tick value using the appropriate precision, assuming
+   * base 10.
+   *
+   * @function
+   * @name pv.Scale.log.prototype.tickFormat
+   * @param {number} t a tick value.
+   * @return {string} a formatted tick value.
+   */
+  scale.tickFormat = function(t) {
+    return t.toPrecision(1);
+  };
+
+  /**
+   * "Nices" this scale, extending the bounds of the input domain to
+   * evenly-rounded values. This method uses {@link pv.logFloor} and {@link
+   * pv.logCeil}. Nicing is useful if the domain is computed dynamically from
+   * data, and may be irregular. For example, given a domain of
+   * [0.20147987687960267, 0.996679553296417], a call to <tt>nice()</tt> might
+   * extend the domain to [0.1, 1].
+   *
+   * <p>This method must be invoked each time after setting the domain (and
+   * base).
+   *
+   * @function
+   * @name pv.Scale.log.prototype.nice
+   * @returns {pv.Scale.log} <tt>this</tt>.
+   */
+  scale.nice = function() {
+    // TODO: support multiple domains
+    d = [pv.logFloor(d[0], b), pv.logCeil(d[1], b)];
+    l = d.map(log);
+    return this;
+  };
+
+  /**
+   * Sets or gets the logarithm base. Defaults to 10.
+   *
+   * @function
+   * @name pv.Scale.log.prototype.base
+   * @param {number} [v] the new base.
+   * @returns {pv.Scale.log} <tt>this</tt>, or the current base.
+   */
+  scale.base = function(v) {
+    if (arguments.length) {
+      b = v;
+      l = d.map(log);
+      return this;
+    }
+    return b;
+  };
+
+  /**
+   * Returns a view of this scale by the specified accessor function <tt>f</tt>.
+   * Given a scale <tt>y</tt>, <tt>y.by(function(d) d.foo)</tt> is equivalent to
+   * <tt>function(d) y(d.foo)</tt>.
+   *
+   * <p>This method is provided for convenience, such that scales can be
+   * succinctly defined inline. For example, given an array of data elements
+   * that have a <tt>score</tt> attribute with the domain [0, 1], the height
+   * property could be specified as:
+   *
+   * <pre>.height(pv.Scale.log().range(0, 480).by(function(d) d.score))</pre>
+   *
+   * This is equivalent to:
+   *
+   * <pre>.height(function(d) d.score * 480)</pre>
+   *
+   * This method should be used judiciously; it is typically more clear to
+   * invoke the scale directly, passing in the value to be scaled.
+   *
+   * @function
+   * @name pv.Scale.log.prototype.by
+   * @param {function} f an accessor function.
+   * @returns {pv.Scale.log} a view of this scale by the specified accessor
+   * function.
+   */
+  scale.by = function(f) {
+    function by() { return scale(f.apply(this, arguments)); }
+    for (var method in scale) by[method] = scale[method];
+    return by;
+  };
+
+  scale.domain.apply(scale, arguments);
+  return scale;
+};
+/**
+ * Returns an ordinal scale for the specified domain. The arguments to this
+ * constructor are optional, and equivalent to calling {@link #domain}.
+ *
+ * @class Represents an ordinal scale. <style
+ * type="text/css">sub{line-height:0}</style> An ordinal scale represents a
+ * pairwise mapping from <i>n</i> discrete values in the input domain to
+ * <i>n</i> discrete values in the output range. For example, an ordinal scale
+ * might map a domain of species ["setosa", "versicolor", "virginica"] to colors
+ * ["red", "green", "blue"]. Thus, saying
+ *
+ * <pre>.fillStyle(function(d) {
+ *     switch (d.species) {
+ *       case "setosa": return "red";
+ *       case "versicolor": return "green";
+ *       case "virginica": return "blue";
+ *     }
+ *   })</pre>
+ *
+ * is equivalent to
+ *
+ * <pre>.fillStyle(pv.Scale.ordinal("setosa", "versicolor", "virginica")
+ *     .range("red", "green", "blue")
+ *     .by(function(d) d.species))</pre>
+ *
+ * If the mapping from species to color does not need to be specified
+ * explicitly, the domain can be omitted. In this case it will be inferred
+ * lazily from the data:
+ *
+ * <pre>.fillStyle(pv.colors("red", "green", "blue")
+ *     .by(function(d) d.species))</pre>
+ *
+ * When the domain is inferred, the first time the scale is invoked, the first
+ * element from the range will be returned. Subsequent calls with unique values
+ * will return subsequent elements from the range. If the inferred domain grows
+ * larger than the range, range values will be reused. However, it is strongly
+ * recommended that the domain and the range contain the same number of
+ * elements.
+ *
+ * <p>A range can be discretized from a continuous interval (e.g., for pixel
+ * positioning) by using {@link #split}, {@link #splitFlush} or
+ * {@link #splitBanded} after the domain has been set. For example, if
+ * <tt>states</tt> is an array of the fifty U.S. state names, the state name can
+ * be encoded in the left position:
+ *
+ * <pre>.left(pv.Scale.ordinal(states)
+ *     .split(0, 640)
+ *     .by(function(d) d.state))</pre>
+ *
+ * <p>N.B.: ordinal scales are not invertible (at least not yet), since the
+ * domain and range and discontinuous. A workaround is to use a linear scale.
+ *
+ * @param {...} domain... domain values.
+ * @returns {pv.Scale.ordinal} an ordinal scale.
+ * @see pv.colors
+ */
+pv.Scale.ordinal = function() {
+  var d = [], i = {}, r = [], band = 0;
+
+  /** @private */
+  function scale(x) {
+    if (!(x in i)) i[x] = d.push(x) - 1;
+    return r[i[x] % r.length];
+  }
+
+  /**
+   * Sets or gets the input domain. This method can be invoked several ways:
+   *
+   * <p>1. <tt>domain(values...)</tt>
+   *
+   * <p>Specifying the domain as a series of values is the most explicit and
+   * recommended approach. However, if the domain values are derived from data,
+   * you may find the second method more appropriate.
+   *
+   * <p>2. <tt>domain(array, f)</tt>
+   *
+   * <p>Rather than enumerating the domain values as explicit arguments to this
+   * method, you can specify a single argument of an array. In addition, you can
+   * specify an optional accessor function to extract the domain values from the
+   * array.
+   *
+   * <p>3. <tt>domain()</tt>
+   *
+   * <p>Invoking the <tt>domain</tt> method with no arguments returns the
+   * current domain as an array.
+   *
+   * @function
+   * @name pv.Scale.ordinal.prototype.domain
+   * @param {...} domain... domain values.
+   * @returns {pv.Scale.ordinal} <tt>this</tt>, or the current domain.
+   */
+  scale.domain = function(array, f) {
+    if (arguments.length) {
+      array = (array instanceof Array)
+          ? ((arguments.length > 1) ? map(array, f) : array)
+          : Array.prototype.slice.call(arguments);
+
+      /* Filter the specified ordinals to their unique values. */
+      d = [];
+      var seen = {};
+      for (var j = 0; j < array.length; j++) {
+        var o = array[j];
+        if (!(o in seen)) {
+          seen[o] = true;
+          d.push(o);
+        }
+      }
+
+      i = pv.numerate(d);
+      return this;
+    }
+    return d;
+  };
+
+  /**
+   * Sets or gets the output range. This method can be invoked several ways:
+   *
+   * <p>1. <tt>range(values...)</tt>
+   *
+   * <p>Specifying the range as a series of values is the most explicit and
+   * recommended approach. However, if the range values are derived from data,
+   * you may find the second method more appropriate.
+   *
+   * <p>2. <tt>range(array, f)</tt>
+   *
+   * <p>Rather than enumerating the range values as explicit arguments to this
+   * method, you can specify a single argument of an array. In addition, you can
+   * specify an optional accessor function to extract the range values from the
+   * array.
+   *
+   * <p>3. <tt>range()</tt>
+   *
+   * <p>Invoking the <tt>range</tt> method with no arguments returns the
+   * current range as an array.
+   *
+   * @function
+   * @name pv.Scale.ordinal.prototype.range
+   * @param {...} range... range values.
+   * @returns {pv.Scale.ordinal} <tt>this</tt>, or the current range.
+   */
+  scale.range = function(array, f) {
+    if (arguments.length) {
+      r = (array instanceof Array)
+          ? ((arguments.length > 1) ? map(array, f) : array)
+          : Array.prototype.slice.call(arguments);
+      if (typeof r[0] == "string") r = r.map(pv.color);
+      return this;
+    }
+    return r;
+  };
+
+  /**
+   * Sets the range from the given continuous interval. The interval
+   * [<i>min</i>, <i>max</i>] is subdivided into <i>n</i> equispaced points,
+   * where <i>n</i> is the number of (unique) values in the domain. The first
+   * and last point are offset from the edge of the range by half the distance
+   * between points.
+   *
+   * <p>This method must be called <i>after</i> the domain is set.
+   *
+   * @function
+   * @name pv.Scale.ordinal.prototype.split
+   * @param {number} min minimum value of the output range.
+   * @param {number} max maximum value of the output range.
+   * @returns {pv.Scale.ordinal} <tt>this</tt>.
+   * @see #splitFlush
+   * @see #splitBanded
+   */
+  scale.split = function(min, max) {
+    var step = (max - min) / this.domain().length;
+    r = pv.range(min + step / 2, max, step);
+    return this;
+  };
+
+  /**
+   * Sets the range from the given continuous interval. The interval
+   * [<i>min</i>, <i>max</i>] is subdivided into <i>n</i> equispaced points,
+   * where <i>n</i> is the number of (unique) values in the domain. The first
+   * and last point are exactly on the edge of the range.
+   *
+   * <p>This method must be called <i>after</i> the domain is set.
+   *
+   * @function
+   * @name pv.Scale.ordinal.prototype.splitFlush
+   * @param {number} min minimum value of the output range.
+   * @param {number} max maximum value of the output range.
+   * @returns {pv.Scale.ordinal} <tt>this</tt>.
+   * @see #split
+   */
+  scale.splitFlush = function(min, max) {
+    var n = this.domain().length, step = (max - min) / (n - 1);
+    r = (n == 1) ? [(min + max) / 2]
+        : pv.range(min, max + step / 2, step);
+    return this;
+  };
+
+  /**
+   * Sets the range from the given continuous interval. The interval
+   * [<i>min</i>, <i>max</i>] is subdivided into <i>n</i> equispaced bands,
+   * where <i>n</i> is the number of (unique) values in the domain. The first
+   * and last band are offset from the edge of the range by the distance between
+   * bands.
+   *
+   * <p>The band width argument, <tt>band</tt>, is typically in the range [0, 1]
+   * and defaults to 1. This fraction corresponds to the amount of space in the
+   * range to allocate to the bands, as opposed to padding. A value of 0.5 means
+   * that the band width will be equal to the padding width. The computed
+   * absolute band width can be retrieved from the range as
+   * <tt>scale.range().band</tt>.
+   *
+   * <p>If the band width argument is negative, this method will allocate bands
+   * of a <i>fixed</i> width <tt>-band</tt>, rather than a relative fraction of
+   * the available space.
+   *
+   * <p>Tip: to inset the bands by a fixed amount <tt>p</tt>, specify a minimum
+   * value of <tt>min + p</tt> (or simply <tt>p</tt>, if <tt>min</tt> is
+   * 0). Then set the mark width to <tt>scale.range().band - p</tt>.
+   *
+   * <p>This method must be called <i>after</i> the domain is set.
+   *
+   * @function
+   * @name pv.Scale.ordinal.prototype.splitBanded
+   * @param {number} min minimum value of the output range.
+   * @param {number} max maximum value of the output range.
+   * @param {number} [band] the fractional band width in [0, 1]; defaults to 1.
+   * @returns {pv.Scale.ordinal} <tt>this</tt>.
+   * @see #split
+   */
+  scale.splitBanded = function(min, max, band) {
+    if (arguments.length < 3) band = 1;
+    if (band < 0) {
+      var n = this.domain().length,
+          total = -band * n,
+          remaining = max - min - total,
+          padding = remaining / (n + 1);
+      r = pv.range(min + padding, max, padding - band);
+      r.band = -band;
+    } else {
+      var step = (max - min) / (this.domain().length + (1 - band));
+      r = pv.range(min + step * (1 - band), max, step);
+      r.band = step * band;
+    }
+    return this;
+  };
+
+  /**
+   * Returns a view of this scale by the specified accessor function <tt>f</tt>.
+   * Given a scale <tt>y</tt>, <tt>y.by(function(d) d.foo)</tt> is equivalent to
+   * <tt>function(d) y(d.foo)</tt>. This method should be used judiciously; it
+   * is typically more clear to invoke the scale directly, passing in the value
+   * to be scaled.
+   *
+   * @function
+   * @name pv.Scale.ordinal.prototype.by
+   * @param {function} f an accessor function.
+   * @returns {pv.Scale.ordinal} a view of this scale by the specified accessor
+   * function.
+   */
+  scale.by = function(f) {
+    function by() { return scale(f.apply(this, arguments)); }
+    for (var method in scale) by[method] = scale[method];
+    return by;
+  };
+
+  scale.domain.apply(scale, arguments);
+  return scale;
+};
+/**
+ * Returns the {@link pv.Color} for the specified color format string. Colors
+ * may have an associated opacity, or alpha channel. Color formats are specified
+ * by CSS Color Modular Level 3, using either in RGB or HSL color space. For
+ * example:<ul>
+ *
+ * <li>#f00 // #rgb
+ * <li>#ff0000 // #rrggbb
+ * <li>rgb(255, 0, 0)
+ * <li>rgb(100%, 0%, 0%)
+ * <li>hsl(0, 100%, 50%)
+ * <li>rgba(0, 0, 255, 0.5)
+ * <li>hsla(120, 100%, 50%, 1)
+ *
+ * </ul>The SVG 1.0 color keywords names are also supported, such as "aliceblue"
+ * and "yellowgreen". The "transparent" keyword is supported for a
+ * fully-transparent color.
+ *
+ * <p>If the <tt>format</tt> argument is already an instance of <tt>Color</tt>,
+ * the argument is returned with no further processing.
+ *
+ * @param {string} format the color specification string, such as "#f00".
+ * @returns {pv.Color} the corresponding <tt>Color</tt>.
+ * @see <a href="http://www.w3.org/TR/SVG/types.html#ColorKeywords">SVG color
+ * keywords</a>
+ * @see <a href="http://www.w3.org/TR/css3-color/">CSS3 color module</a>
+ */
+pv.color = function(format) {
+  if (!format || (format == "transparent")) {
+    return pv.rgb(0, 0, 0, 0);
+  }
+  if (format instanceof pv.Color) {
+    return format;
+  }
+
+  /* Handle hsl, rgb. */
+  var m1 = /([a-z]+)\((.*)\)/i.exec(format);
+  if (m1) {
+    var m2 = m1[2].split(","), a = 1;
+    switch (m1[1]) {
+      case "hsla":
+      case "rgba": {
+        a = parseFloat(m2[3]);
+        break;
+      }
+    }
+    switch (m1[1]) {
+      case "hsla":
+      case "hsl": {
+        var h = parseFloat(m2[0]), // degrees
+            s = parseFloat(m2[1]) / 100, // percentage
+            l = parseFloat(m2[2]) / 100; // percentage
+        return (new pv.Color.Hsl(h, s, l, a)).rgb();
+      }
+      case "rgba":
+      case "rgb": {
+        function parse(c) { // either integer or percentage
+          var f = parseFloat(c);
+          return (c[c.length - 1] == '%') ? Math.round(f * 2.55) : f;
+        }
+        var r = parse(m2[0]), g = parse(m2[1]), b = parse(m2[2]);
+        return pv.rgb(r, g, b, a);
+      }
+    }
+  }
+
+  /* Named colors. */
+  format = pv.Color.names[format] || format;
+
+  /* Hexadecimal colors: #rgb and #rrggbb. */
+  if (format.charAt(0) == "#") {
+    var r, g, b;
+    if (format.length == 4) {
+      r = format.charAt(1); r += r;
+      g = format.charAt(2); g += g;
+      b = format.charAt(3); b += b;
+    } else if (format.length == 7) {
+      r = format.substring(1, 3);
+      g = format.substring(3, 5);
+      b = format.substring(5, 7);
+    }
+    return pv.rgb(parseInt(r, 16), parseInt(g, 16), parseInt(b, 16), 1);
+  }
+
+  /* Otherwise, assume named colors. TODO allow lazy conversion to RGB. */
+  return new pv.Color(format, 1);
+};
+
+/**
+ * Constructs a color with the specified color format string and opacity. This
+ * constructor should not be invoked directly; use {@link pv.color} instead.
+ *
+ * @class Represents an abstract (possibly translucent) color. The color is
+ * divided into two parts: the <tt>color</tt> attribute, an opaque color format
+ * string, and the <tt>opacity</tt> attribute, a float in [0, 1]. The color
+ * space is dependent on the implementing class; all colors support the
+ * {@link #rgb} method to convert to RGB color space for interpolation.
+ *
+ * <p>See also the <a href="../../api/Color.html">Color guide</a>.
+ *
+ * @param {string} color an opaque color format string, such as "#f00".
+ * @param {number} opacity the opacity, in [0,1].
+ * @see pv.color
+ */
+pv.Color = function(color, opacity) {
+  /**
+   * An opaque color format string, such as "#f00".
+   *
+   * @type string
+   * @see <a href="http://www.w3.org/TR/SVG/types.html#ColorKeywords">SVG color
+   * keywords</a>
+   * @see <a href="http://www.w3.org/TR/css3-color/">CSS3 color module</a>
+   */
+  this.color = color;
+
+  /**
+   * The opacity, a float in [0, 1].
+   *
+   * @type number
+   */
+  this.opacity = opacity;
+};
+
+/**
+ * Returns a new color that is a brighter version of this color. The behavior of
+ * this method may vary slightly depending on the underlying color space.
+ * Although brighter and darker are inverse operations, the results of a series
+ * of invocations of these two methods might be inconsistent because of rounding
+ * errors.
+ *
+ * @param [k] {number} an optional scale factor; defaults to 1.
+ * @see #darker
+ * @returns {pv.Color} a brighter color.
+ */
+pv.Color.prototype.brighter = function(k) {
+  return this.rgb().brighter(k);
+};
+
+/**
+ * Returns a new color that is a brighter version of this color. The behavior of
+ * this method may vary slightly depending on the underlying color space.
+ * Although brighter and darker are inverse operations, the results of a series
+ * of invocations of these two methods might be inconsistent because of rounding
+ * errors.
+ *
+ * @param [k] {number} an optional scale factor; defaults to 1.
+ * @see #brighter
+ * @returns {pv.Color} a darker color.
+ */
+pv.Color.prototype.darker = function(k) {
+  return this.rgb().darker(k);
+};
+
+/**
+ * Constructs a new RGB color with the specified channel values.
+ *
+ * @param {number} r the red channel, an integer in [0,255].
+ * @param {number} g the green channel, an integer in [0,255].
+ * @param {number} b the blue channel, an integer in [0,255].
+ * @param {number} [a] the alpha channel, a float in [0,1].
+ * @returns pv.Color.Rgb
+ */
+pv.rgb = function(r, g, b, a) {
+  return new pv.Color.Rgb(r, g, b, (arguments.length == 4) ? a : 1);
+};
+
+/**
+ * Constructs a new RGB color with the specified channel values.
+ *
+ * @class Represents a color in RGB space.
+ *
+ * @param {number} r the red channel, an integer in [0,255].
+ * @param {number} g the green channel, an integer in [0,255].
+ * @param {number} b the blue channel, an integer in [0,255].
+ * @param {number} a the alpha channel, a float in [0,1].
+ * @extends pv.Color
+ */
+pv.Color.Rgb = function(r, g, b, a) {
+  pv.Color.call(this, a ? ("rgb(" + r + "," + g + "," + b + ")") : "none", a);
+
+  /**
+   * The red channel, an integer in [0, 255].
+   *
+   * @type number
+   */
+  this.r = r;
+
+  /**
+   * The green channel, an integer in [0, 255].
+   *
+   * @type number
+   */
+  this.g = g;
+
+  /**
+   * The blue channel, an integer in [0, 255].
+   *
+   * @type number
+   */
+  this.b = b;
+
+  /**
+   * The alpha channel, a float in [0, 1].
+   *
+   * @type number
+   */
+  this.a = a;
+};
+pv.Color.Rgb.prototype = pv.extend(pv.Color);
+
+/**
+ * Constructs a new RGB color with the same green, blue and alpha channels as
+ * this color, with the specified red channel.
+ *
+ * @param {number} r the red channel, an integer in [0,255].
+ */
+pv.Color.Rgb.prototype.red = function(r) {
+  return pv.rgb(r, this.g, this.b, this.a);
+};
+
+/**
+ * Constructs a new RGB color with the same red, blue and alpha channels as this
+ * color, with the specified green channel.
+ *
+ * @param {number} g the green channel, an integer in [0,255].
+ */
+pv.Color.Rgb.prototype.green = function(g) {
+  return pv.rgb(this.r, g, this.b, this.a);
+};
+
+/**
+ * Constructs a new RGB color with the same red, green and alpha channels as
+ * this color, with the specified blue channel.
+ *
+ * @param {number} b the blue channel, an integer in [0,255].
+ */
+pv.Color.Rgb.prototype.blue = function(b) {
+  return pv.rgb(this.r, this.g, b, this.a);
+};
+
+/**
+ * Constructs a new RGB color with the same red, green and blue channels as this
+ * color, with the specified alpha channel.
+ *
+ * @param {number} a the alpha channel, a float in [0,1].
+ */
+pv.Color.Rgb.prototype.alpha = function(a) {
+  return pv.rgb(this.r, this.g, this.b, a);
+};
+
+/**
+ * Returns the RGB color equivalent to this color. This method is abstract and
+ * must be implemented by subclasses.
+ *
+ * @returns {pv.Color.Rgb} an RGB color.
+ * @function
+ * @name pv.Color.prototype.rgb
+ */
+
+/**
+ * Returns this.
+ *
+ * @returns {pv.Color.Rgb} this.
+ */
+pv.Color.Rgb.prototype.rgb = function() { return this; };
+
+/**
+ * Returns a new color that is a brighter version of this color. This method
+ * applies an arbitrary scale factor to each of the three RGB components of this
+ * color to create a brighter version of this color. Although brighter and
+ * darker are inverse operations, the results of a series of invocations of
+ * these two methods might be inconsistent because of rounding errors.
+ *
+ * @param [k] {number} an optional scale factor; defaults to 1.
+ * @see #darker
+ * @returns {pv.Color.Rgb} a brighter color.
+ */
+pv.Color.Rgb.prototype.brighter = function(k) {
+  k = Math.pow(0.7, arguments.length ? k : 1);
+  var r = this.r, g = this.g, b = this.b, i = 30;
+  if (!r && !g && !b) return pv.rgb(i, i, i, this.a);
+  if (r && (r < i)) r = i;
+  if (g && (g < i)) g = i;
+  if (b && (b < i)) b = i;
+  return pv.rgb(
+      Math.min(255, Math.floor(r / k)),
+      Math.min(255, Math.floor(g / k)),
+      Math.min(255, Math.floor(b / k)),
+      this.a);
+};
+
+/**
+ * Returns a new color that is a darker version of this color. This method
+ * applies an arbitrary scale factor to each of the three RGB components of this
+ * color to create a darker version of this color. Although brighter and darker
+ * are inverse operations, the results of a series of invocations of these two
+ * methods might be inconsistent because of rounding errors.
+ *
+ * @param [k] {number} an optional scale factor; defaults to 1.
+ * @see #brighter
+ * @returns {pv.Color.Rgb} a darker color.
+ */
+pv.Color.Rgb.prototype.darker = function(k) {
+  k = Math.pow(0.7, arguments.length ? k : 1);
+  return pv.rgb(
+      Math.max(0, Math.floor(k * this.r)),
+      Math.max(0, Math.floor(k * this.g)),
+      Math.max(0, Math.floor(k * this.b)),
+      this.a);
+};
+
+/**
+ * Constructs a new HSL color with the specified values.
+ *
+ * @param {number} h the hue, an integer in [0, 360].
+ * @param {number} s the saturation, a float in [0, 1].
+ * @param {number} l the lightness, a float in [0, 1].
+ * @param {number} [a] the opacity, a float in [0, 1].
+ * @returns pv.Color.Hsl
+ */
+pv.hsl = function(h, s, l, a) {
+  return new pv.Color.Hsl(h, s, l,  (arguments.length == 4) ? a : 1);
+};
+
+/**
+ * Constructs a new HSL color with the specified values.
+ *
+ * @class Represents a color in HSL space.
+ *
+ * @param {number} h the hue, an integer in [0, 360].
+ * @param {number} s the saturation, a float in [0, 1].
+ * @param {number} l the lightness, a float in [0, 1].
+ * @param {number} a the opacity, a float in [0, 1].
+ * @extends pv.Color
+ */
+pv.Color.Hsl = function(h, s, l, a) {
+  pv.Color.call(this, "hsl(" + h + "," + (s * 100) + "%," + (l * 100) + "%)", a);
+
+  /**
+   * The hue, an integer in [0, 360].
+   *
+   * @type number
+   */
+  this.h = h;
+
+  /**
+   * The saturation, a float in [0, 1].
+   *
+   * @type number
+   */
+  this.s = s;
+
+  /**
+   * The lightness, a float in [0, 1].
+   *
+   * @type number
+   */
+  this.l = l;
+
+  /**
+   * The opacity, a float in [0, 1].
+   *
+   * @type number
+   */
+  this.a = a;
+};
+pv.Color.Hsl.prototype = pv.extend(pv.Color);
+
+/**
+ * Constructs a new HSL color with the same saturation, lightness and alpha as
+ * this color, and the specified hue.
+ *
+ * @param {number} h the hue, an integer in [0, 360].
+ */
+pv.Color.Hsl.prototype.hue = function(h) {
+  return pv.hsl(h, this.s, this.l, this.a);
+};
+
+/**
+ * Constructs a new HSL color with the same hue, lightness and alpha as this
+ * color, and the specified saturation.
+ *
+ * @param {number} s the saturation, a float in [0, 1].
+ */
+pv.Color.Hsl.prototype.saturation = function(s) {
+  return pv.hsl(this.h, s, this.l, this.a);
+};
+
+/**
+ * Constructs a new HSL color with the same hue, saturation and alpha as this
+ * color, and the specified lightness.
+ *
+ * @param {number} l the lightness, a float in [0, 1].
+ */
+pv.Color.Hsl.prototype.lightness = function(l) {
+  return pv.hsl(this.h, this.s, l, this.a);
+};
+
+/**
+ * Constructs a new HSL color with the same hue, saturation and lightness as
+ * this color, and the specified alpha.
+ *
+ * @param {number} a the opacity, a float in [0, 1].
+ */
+pv.Color.Hsl.prototype.alpha = function(a) {
+  return pv.hsl(this.h, this.s, this.l, a);
+};
+
+/**
+ * Returns the RGB color equivalent to this HSL color.
+ *
+ * @returns {pv.Color.Rgb} an RGB color.
+ */
+pv.Color.Hsl.prototype.rgb = function() {
+  var h = this.h, s = this.s, l = this.l;
+
+  /* Some simple corrections for h, s and l. */
+  h = h % 360; if (h < 0) h += 360;
+  s = Math.max(0, Math.min(s, 1));
+  l = Math.max(0, Math.min(l, 1));
+
+  /* From FvD 13.37, CSS Color Module Level 3 */
+  var m2 = (l <= .5) ? (l * (1 + s)) : (l + s - l * s);
+  var m1 = 2 * l - m2;
+  function v(h) {
+    if (h > 360) h -= 360;
+    else if (h < 0) h += 360;
+    if (h < 60) return m1 + (m2 - m1) * h / 60;
+    if (h < 180) return m2;
+    if (h < 240) return m1 + (m2 - m1) * (240 - h) / 60;
+    return m1;
+  }
+  function vv(h) {
+    return Math.round(v(h) * 255);
+  }
+
+  return pv.rgb(vv(h + 120), vv(h), vv(h - 120), this.a);
+};
+
+/**
+ * @private SVG color keywords, per CSS Color Module Level 3.
+ *
+ * @see <a href="http://www.w3.org/TR/SVG/types.html#ColorKeywords">SVG color
+ * keywords</a>
+ */
+pv.Color.names = {
+  aliceblue: "#f0f8ff",
+  antiquewhite: "#faebd7",
+  aqua: "#00ffff",
+  aquamarine: "#7fffd4",
+  azure: "#f0ffff",
+  beige: "#f5f5dc",
+  bisque: "#ffe4c4",
+  black: "#000000",
+  blanchedalmond: "#ffebcd",
+  blue: "#0000ff",
+  blueviolet: "#8a2be2",
+  brown: "#a52a2a",
+  burlywood: "#deb887",
+  cadetblue: "#5f9ea0",
+  chartreuse: "#7fff00",
+  chocolate: "#d2691e",
+  coral: "#ff7f50",
+  cornflowerblue: "#6495ed",
+  cornsilk: "#fff8dc",
+  crimson: "#dc143c",
+  cyan: "#00ffff",
+  darkblue: "#00008b",
+  darkcyan: "#008b8b",
+  darkgoldenrod: "#b8860b",
+  darkgray: "#a9a9a9",
+  darkgreen: "#006400",
+  darkgrey: "#a9a9a9",
+  darkkhaki: "#bdb76b",
+  darkmagenta: "#8b008b",
+  darkolivegreen: "#556b2f",
+  darkorange: "#ff8c00",
+  darkorchid: "#9932cc",
+  darkred: "#8b0000",
+  darksalmon: "#e9967a",
+  darkseagreen: "#8fbc8f",
+  darkslateblue: "#483d8b",
+  darkslategray: "#2f4f4f",
+  darkslategrey: "#2f4f4f",
+  darkturquoise: "#00ced1",
+  darkviolet: "#9400d3",
+  deeppink: "#ff1493",
+  deepskyblue: "#00bfff",
+  dimgray: "#696969",
+  dimgrey: "#696969",
+  dodgerblue: "#1e90ff",
+  firebrick: "#b22222",
+  floralwhite: "#fffaf0",
+  forestgreen: "#228b22",
+  fuchsia: "#ff00ff",
+  gainsboro: "#dcdcdc",
+  ghostwhite: "#f8f8ff",
+  gold: "#ffd700",
+  goldenrod: "#daa520",
+  gray: "#808080",
+  green: "#008000",
+  greenyellow: "#adff2f",
+  grey: "#808080",
+  honeydew: "#f0fff0",
+  hotpink: "#ff69b4",
+  indianred: "#cd5c5c",
+  indigo: "#4b0082",
+  ivory: "#fffff0",
+  khaki: "#f0e68c",
+  lavender: "#e6e6fa",
+  lavenderblush: "#fff0f5",
+  lawngreen: "#7cfc00",
+  lemonchiffon: "#fffacd",
+  lightblue: "#add8e6",
+  lightcoral: "#f08080",
+  lightcyan: "#e0ffff",
+  lightgoldenrodyellow: "#fafad2",
+  lightgray: "#d3d3d3",
+  lightgreen: "#90ee90",
+  lightgrey: "#d3d3d3",
+  lightpink: "#ffb6c1",
+  lightsalmon: "#ffa07a",
+  lightseagreen: "#20b2aa",
+  lightskyblue: "#87cefa",
+  lightslategray: "#778899",
+  lightslategrey: "#778899",
+  lightsteelblue: "#b0c4de",
+  lightyellow: "#ffffe0",
+  lime: "#00ff00",
+  limegreen: "#32cd32",
+  linen: "#faf0e6",
+  magenta: "#ff00ff",
+  maroon: "#800000",
+  mediumaquamarine: "#66cdaa",
+  mediumblue: "#0000cd",
+  mediumorchid: "#ba55d3",
+  mediumpurple: "#9370db",
+  mediumseagreen: "#3cb371",
+  mediumslateblue: "#7b68ee",
+  mediumspringgreen: "#00fa9a",
+  mediumturquoise: "#48d1cc",
+  mediumvioletred: "#c71585",
+  midnightblue: "#191970",
+  mintcream: "#f5fffa",
+  mistyrose: "#ffe4e1",
+  moccasin: "#ffe4b5",
+  navajowhite: "#ffdead",
+  navy: "#000080",
+  oldlace: "#fdf5e6",
+  olive: "#808000",
+  olivedrab: "#6b8e23",
+  orange: "#ffa500",
+  orangered: "#ff4500",
+  orchid: "#da70d6",
+  palegoldenrod: "#eee8aa",
+  palegreen: "#98fb98",
+  paleturquoise: "#afeeee",
+  palevioletred: "#db7093",
+  papayawhip: "#ffefd5",
+  peachpuff: "#ffdab9",
+  peru: "#cd853f",
+  pink: "#ffc0cb",
+  plum: "#dda0dd",
+  powderblue: "#b0e0e6",
+  purple: "#800080",
+  red: "#ff0000",
+  rosybrown: "#bc8f8f",
+  royalblue: "#4169e1",
+  saddlebrown: "#8b4513",
+  salmon: "#fa8072",
+  sandybrown: "#f4a460",
+  seagreen: "#2e8b57",
+  seashell: "#fff5ee",
+  sienna: "#a0522d",
+  silver: "#c0c0c0",
+  skyblue: "#87ceeb",
+  slateblue: "#6a5acd",
+  slategray: "#708090",
+  slategrey: "#708090",
+  snow: "#fffafa",
+  springgreen: "#00ff7f",
+  steelblue: "#4682b4",
+  tan: "#d2b48c",
+  teal: "#008080",
+  thistle: "#d8bfd8",
+  tomato: "#ff6347",
+  turquoise: "#40e0d0",
+  violet: "#ee82ee",
+  wheat: "#f5deb3",
+  white: "#ffffff",
+  whitesmoke: "#f5f5f5",
+  yellow: "#ffff00",
+  yellowgreen: "#9acd32"
+};
+/**
+ * Returns a new categorical color encoding using the specified colors.  The
+ * arguments to this method are an array of colors; see {@link pv.color}. For
+ * example, to create a categorical color encoding using the <tt>species</tt>
+ * attribute:
+ *
+ * <pre>pv.colors("red", "green", "blue").by(function(d) d.species)</pre>
+ *
+ * The result of this expression can be used as a fill- or stroke-style
+ * property. This assumes that the data's <tt>species</tt> attribute is a
+ * string.
+ *
+ * @param {string} colors... categorical colors.
+ * @see pv.Scale.ordinal
+ * @returns {pv.Scale.ordinal} an ordinal color scale.
+ */
+pv.colors = function() {
+  var scale = pv.Scale.ordinal();
+  scale.range.apply(scale, arguments);
+  return scale;
+};
+
+/**
+ * A collection of standard color palettes for categorical encoding.
+ *
+ * @namespace A collection of standard color palettes for categorical encoding.
+ */
+pv.Colors = {};
+
+/**
+ * Returns a new 10-color scheme. The arguments to this constructor are
+ * optional, and equivalent to calling {@link pv.Scale.OrdinalScale#domain}. The
+ * following colors are used:
+ *
+ * <div style="background:#1f77b4;">#1f77b4</div>
+ * <div style="background:#ff7f0e;">#ff7f0e</div>
+ * <div style="background:#2ca02c;">#2ca02c</div>
+ * <div style="background:#d62728;">#d62728</div>
+ * <div style="background:#9467bd;">#9467bd</div>
+ * <div style="background:#8c564b;">#8c564b</div>
+ * <div style="background:#e377c2;">#e377c2</div>
+ * <div style="background:#7f7f7f;">#7f7f7f</div>
+ * <div style="background:#bcbd22;">#bcbd22</div>
+ * <div style="background:#17becf;">#17becf</div>
+ *
+ * @param {number...} domain... domain values.
+ * @returns {pv.Scale.ordinal} a new ordinal color scale.
+ * @see pv.color
+ */
+pv.Colors.category10 = function() {
+  var scale = pv.colors(
+      "#1f77b4", "#ff7f0e", "#2ca02c", "#d62728", "#9467bd",
+      "#8c564b", "#e377c2", "#7f7f7f", "#bcbd22", "#17becf");
+  scale.domain.apply(scale, arguments);
+  return scale;
+};
+
+/**
+ * Returns a new 20-color scheme. The arguments to this constructor are
+ * optional, and equivalent to calling {@link pv.Scale.OrdinalScale#domain}. The
+ * following colors are used:
+ *
+ * <div style="background:#1f77b4;">#1f77b4</div>
+ * <div style="background:#aec7e8;">#aec7e8</div>
+ * <div style="background:#ff7f0e;">#ff7f0e</div>
+ * <div style="background:#ffbb78;">#ffbb78</div>
+ * <div style="background:#2ca02c;">#2ca02c</div>
+ * <div style="background:#98df8a;">#98df8a</div>
+ * <div style="background:#d62728;">#d62728</div>
+ * <div style="background:#ff9896;">#ff9896</div>
+ * <div style="background:#9467bd;">#9467bd</div>
+ * <div style="background:#c5b0d5;">#c5b0d5</div>
+ * <div style="background:#8c564b;">#8c564b</div>
+ * <div style="background:#c49c94;">#c49c94</div>
+ * <div style="background:#e377c2;">#e377c2</div>
+ * <div style="background:#f7b6d2;">#f7b6d2</div>
+ * <div style="background:#7f7f7f;">#7f7f7f</div>
+ * <div style="background:#c7c7c7;">#c7c7c7</div>
+ * <div style="background:#bcbd22;">#bcbd22</div>
+ * <div style="background:#dbdb8d;">#dbdb8d</div>
+ * <div style="background:#17becf;">#17becf</div>
+ * <div style="background:#9edae5;">#9edae5</div>
+ *
+ * @param {number...} domain... domain values.
+ * @returns {pv.Scale.ordinal} a new ordinal color scale.
+ * @see pv.color
+*/
+pv.Colors.category20 = function() {
+  var scale = pv.colors(
+      "#1f77b4", "#aec7e8", "#ff7f0e", "#ffbb78", "#2ca02c",
+      "#98df8a", "#d62728", "#ff9896", "#9467bd", "#c5b0d5",
+      "#8c564b", "#c49c94", "#e377c2", "#f7b6d2", "#7f7f7f",
+      "#c7c7c7", "#bcbd22", "#dbdb8d", "#17becf", "#9edae5");
+  scale.domain.apply(scale, arguments);
+  return scale;
+};
+
+/**
+ * Returns a new alternative 19-color scheme. The arguments to this constructor
+ * are optional, and equivalent to calling
+ * {@link pv.Scale.OrdinalScale#domain}. The following colors are used:
+ *
+ * <div style="background:#9c9ede;">#9c9ede</div>
+ * <div style="background:#7375b5;">#7375b5</div>
+ * <div style="background:#4a5584;">#4a5584</div>
+ * <div style="background:#cedb9c;">#cedb9c</div>
+ * <div style="background:#b5cf6b;">#b5cf6b</div>
+ * <div style="background:#8ca252;">#8ca252</div>
+ * <div style="background:#637939;">#637939</div>
+ * <div style="background:#e7cb94;">#e7cb94</div>
+ * <div style="background:#e7ba52;">#e7ba52</div>
+ * <div style="background:#bd9e39;">#bd9e39</div>
+ * <div style="background:#8c6d31;">#8c6d31</div>
+ * <div style="background:#e7969c;">#e7969c</div>
+ * <div style="background:#d6616b;">#d6616b</div>
+ * <div style="background:#ad494a;">#ad494a</div>
+ * <div style="background:#843c39;">#843c39</div>
+ * <div style="background:#de9ed6;">#de9ed6</div>
+ * <div style="background:#ce6dbd;">#ce6dbd</div>
+ * <div style="background:#a55194;">#a55194</div>
+ * <div style="background:#7b4173;">#7b4173</div>
+ *
+ * @param {number...} domain... domain values.
+ * @returns {pv.Scale.ordinal} a new ordinal color scale.
+ * @see pv.color
+ */
+pv.Colors.category19 = function() {
+  var scale = pv.colors(
+      "#9c9ede", "#7375b5", "#4a5584", "#cedb9c", "#b5cf6b",
+      "#8ca252", "#637939", "#e7cb94", "#e7ba52", "#bd9e39",
+      "#8c6d31", "#e7969c", "#d6616b", "#ad494a", "#843c39",
+      "#de9ed6", "#ce6dbd", "#a55194", "#7b4173");
+  scale.domain.apply(scale, arguments);
+  return scale;
+};
+/**
+ * Returns a linear color ramp from the specified <tt>start</tt> color to the
+ * specified <tt>end</tt> color. The color arguments may be specified either as
+ * <tt>string</tt>s or as {@link pv.Color}s.
+ *
+ * @param {string} start the start color; may be a <tt>pv.Color</tt>.
+ * @param {string} end the end color; may be a <tt>pv.Color</tt>.
+ * @returns {Function} a color ramp from <tt>start</tt> to <tt>end</tt>.
+ * @see pv.Scale.linear
+ */
+pv.ramp = function(start, end) {
+  var scale = pv.Scale.linear();
+  scale.range.apply(scale, arguments);
+  return scale;
+};
+// TODO don't populate default attributes?
+
+/**
+ * @private
+ * @namespace
+ */
+pv.Scene = pv.SvgScene = {};
+
+/**
+ * Updates the display for the specified array of scene nodes.
+ *
+ * @param scenes {array} an array of scene nodes.
+ */
+pv.SvgScene.updateAll = function(scenes) {
+  if (!scenes.length) return;
+  if ((scenes[0].reverse)
+      && (scenes.type != "line")
+      && (scenes.type != "area")) {
+    var reversed = pv.extend(scenes);
+    for (var i = 0, j = scenes.length - 1; j >= 0; i++, j--) {
+      reversed[i] = scenes[j];
+    }
+    scenes = reversed;
+  }
+  this.removeSiblings(this[scenes.type](scenes));
+};
+
+/**
+ * Creates a new SVG element of the specified type.
+ *
+ * @param type {string} an SVG element type, such as "rect".
+ * @return a new SVG element.
+ */
+pv.SvgScene.create = function(type) {
+  return document.createElementNS(pv.ns.svg, type);
+};
+
+/**
+ * Expects the element <i>e</i> to be the specified type. If the element does
+ * not exist, a new one is created. If the element does exist but is the wrong
+ * type, it is replaced with the specified element.
+ *
+ * @param type {string} an SVG element type, such as "rect".
+ * @return a new SVG element.
+ */
+pv.SvgScene.expect = function(type, e) {
+  if (!e) return this.create(type);
+  if (e.tagName == "a") e = e.firstChild;
+  if (e.tagName == type) return e;
+  var n = this.create(type);
+  e.parentNode.replaceChild(n, e);
+  return n;
+};
+
+/** TODO */
+pv.SvgScene.append = function(e, scenes, index) {
+  e.$scene = {scenes:scenes, index:index};
+  e = this.title(e, scenes[index]);
+  if (!e.parentNode) scenes.$g.appendChild(e);
+  return e.nextSibling;
+};
+
+/**
+ * Applies a title tooltip to the specified element <tt>e</tt>, using the
+ * <tt>title</tt> property of the specified scene node <tt>s</tt>. Note that
+ * this implementation does not create an SVG <tt>title</tt> element as a child
+ * of <tt>e</tt>; although this is the recommended standard, it is only
+ * supported in Opera. Instead, an anchor element is created around the element
+ * <tt>e</tt>, and the <tt>xlink:title</tt> attribute is set accordingly.
+ *
+ * @param e an SVG element.
+ * @param s a scene node.
+ */
+pv.SvgScene.title = function(e, s) {
+  var a = e.parentNode, t = String(s.title);
+  if (a && (a.tagName != "a")) a = null;
+  if (t) {
+    if (!a) {
+      a = this.create("a");
+      if (e.parentNode) e.parentNode.replaceChild(a, e);
+      a.appendChild(e);
+    }
+    a.setAttributeNS(pv.ns.xlink, "title", t);
+    return a;
+  }
+  if (a) a.parentNode.replaceChild(e, a);
+  return e;
+};
+
+/** TODO */
+pv.SvgScene.dispatch = function(e) {
+  var t = e.target.$scene;
+  if (t) {
+    t.scenes.mark.dispatch(e.type, t.scenes, t.index);
+    e.preventDefault();
+  }
+};
+
+/** TODO */
+pv.SvgScene.removeSiblings = function(e) {
+  while (e) {
+    var n = e.nextSibling;
+    e.parentNode.removeChild(e);
+    e = n;
+  }
+};
+// TODO strokeStyle for areaSegment?
+
+pv.SvgScene.area = function(scenes) {
+  var e = scenes.$g.firstChild;
+  if (!scenes.length) return e;
+  var s = scenes[0];
+
+  /* segmented */
+  if (s.segmented) return this.areaSegment(scenes);
+
+  /* visible */
+  if (!s.visible) return e;
+  var fill = pv.color(s.fillStyle), stroke = pv.color(s.strokeStyle);
+  if (!fill.opacity && !stroke.opacity) return e;
+
+  /* points */
+  var p1 = "", p2 = "";
+  for (var i = 0, j = scenes.length - 1; j >= 0; i++, j--) {
+    var si = scenes[i], sj = scenes[j];
+    p1 += si.left + "," + si.top + " ";
+    p2 += (sj.left + sj.width) + "," + (sj.top + sj.height) + " ";
+
+    /* interpolate (assume linear by default) */
+    if (i < scenes.length - 1) {
+      var sk = scenes[i + 1], sl = scenes[j - 1];
+      switch (s.interpolate) {
+        case "step-before": {
+          p1 += si.left + "," + sk.top + " ";
+          p2 += (sl.left + sl.width) + "," + (sj.top + sj.height) + " ";
+          break;
+        }
+        case "step-after": {
+          p1 += sk.left + "," + si.top + " ";
+          p2 += (sj.left + sj.width) + "," + (sl.top + sl.height) + " ";
+          break;
+        }
+      }
+    }
+  }
+
+  e = this.expect("polygon", e);
+  e.setAttribute("cursor", s.cursor);
+  e.setAttribute("points", p1 + p2);
+  var fill = pv.color(s.fillStyle);
+  e.setAttribute("fill", fill.color);
+  e.setAttribute("fill-opacity", fill.opacity);
+  var stroke = pv.color(s.strokeStyle);
+  e.setAttribute("stroke", stroke.color);
+  e.setAttribute("stroke-opacity", stroke.opacity);
+  e.setAttribute("stroke-width", s.lineWidth);
+  return this.append(e, scenes, 0);
+};
+
+pv.SvgScene.areaSegment = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0, n = scenes.length - 1; i < n; i++) {
+    var s1 = scenes[i], s2 = scenes[i + 1];
+
+    /* visible */
+    if (!s1.visible || !s2.visible) continue;
+    var fill = pv.color(s1.fillStyle), stroke = pv.color(s1.strokeStyle);
+    if (!fill.opacity && !stroke.opacity) continue;
+
+    /* points */
+    var p = s1.left + "," + s1.top + " "
+        + s2.left + "," + s2.top + " "
+        + (s2.left + s2.width) + "," + (s2.top + s2.height) + " "
+        + (s1.left + s1.width) + "," + (s1.top + s1.height);
+
+    e = this.expect("polygon", e);
+    e.setAttribute("cursor", s1.cursor);
+    e.setAttribute("points", p);
+    e.setAttribute("fill", fill.color);
+    e.setAttribute("fill-opacity", fill.opacity);
+    e.setAttribute("stroke", stroke.color);
+    e.setAttribute("stroke-opacity", stroke.opacity);
+    e.setAttribute("stroke-width", s1.lineWidth);
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+pv.SvgScene.bar = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0; i < scenes.length; i++) {
+    var s = scenes[i];
+
+    /* visible */
+    if (!s.visible) continue;
+    var fill = pv.color(s.fillStyle), stroke = pv.color(s.strokeStyle);
+    if (!fill.opacity && !stroke.opacity) continue;
+
+    e = this.expect("rect", e);
+    e.setAttribute("cursor", s.cursor);
+    e.setAttribute("x", s.left);
+    e.setAttribute("y", s.top);
+    e.setAttribute("width", Math.max(1E-10, s.width));
+    e.setAttribute("height", Math.max(1E-10, s.height));
+    e.setAttribute("fill", fill.color);
+    e.setAttribute("fill-opacity", fill.opacity);
+    e.setAttribute("stroke", stroke.color);
+    e.setAttribute("stroke-opacity", stroke.opacity);
+    e.setAttribute("stroke-width", s.lineWidth);
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+pv.SvgScene.dot = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0; i < scenes.length; i++) {
+    var s = scenes[i];
+
+    /* visible */
+    if (!s.visible) continue;
+    var fill = pv.color(s.fillStyle), stroke = pv.color(s.strokeStyle);
+    if (!fill.opacity && !stroke.opacity) continue;
+
+    /* points */
+    var radius = Math.sqrt(s.size), fillPath = "", strokePath = "";
+    switch (s.shape) {
+      case "cross": {
+        fillPath = "M" + -radius + "," + -radius
+            + "L" + radius + "," + radius
+            + "M" + radius + "," + -radius
+            + "L" + -radius + "," + radius;
+        break;
+      }
+      case "triangle": {
+        var h = radius, w = radius * 2 / Math.sqrt(3);
+        fillPath = "M0," + h
+            + "L" + w +"," + -h
+            + " " + -w + "," + -h
+            + "Z";
+        break;
+      }
+      case "diamond": {
+        radius *= Math.sqrt(2);
+        fillPath = "M0," + -radius
+            + "L" + radius + ",0"
+            + " 0," + radius
+            + " " + -radius + ",0"
+            + "Z";
+        break;
+      }
+      case "square": {
+        fillPath = "M" + -radius + "," + -radius
+            + "L" + radius + "," + -radius
+            + " " + radius + "," + radius
+            + " " + -radius + "," + radius
+            + "Z";
+        break;
+      }
+      case "tick": {
+        fillPath = "M0,0L0," + -s.size;
+        break;
+      }
+      default: {
+        function circle(r) {
+          return "M0," + r
+              + "A" + r + "," + r + " 0 1,1 0," + (-r)
+              + "A" + r + "," + r + " 0 1,1 0," + r
+              + "Z";
+        }
+        if (s.lineWidth / 2 > radius) strokePath = circle(s.lineWidth);
+        fillPath = circle(radius);
+        break;
+      }
+    }
+
+    /* transform */
+    var transform = "translate(" + s.left + "," + s.top + ")"
+        + (s.angle ? " rotate(" + 180 * s.angle / Math.PI + ")" : "");
+
+    /* The normal fill path. */
+    e = this.expect("path", e);
+    e.setAttribute("d", fillPath);
+    e.setAttribute("transform", transform);
+    e.setAttribute("fill", fill.color);
+    e.setAttribute("fill-opacity", fill.opacity);
+    e.setAttribute("cursor", s.cursor);
+    if (strokePath) {
+      e.setAttribute("stroke", "none");
+    } else {
+      e.setAttribute("stroke", stroke.color);
+      e.setAttribute("stroke-opacity", stroke.opacity);
+      e.setAttribute("stroke-width", s.lineWidth);
+    }
+    e = this.append(e, scenes, i);
+
+    /* The special-case stroke path. */
+    if (strokePath) {
+      e = this.expect("path", e);
+      e.setAttribute("d", strokePath);
+      e.setAttribute("transform", transform);
+      e.setAttribute("fill", stroke.color);
+      e.setAttribute("fill-opacity", stroke.opacity);
+      e.setAttribute("cursor", s.cursor);
+      e = this.append(e, scenes, i);
+    }
+  }
+  return e;
+};
+pv.SvgScene.image = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0; i < scenes.length; i++) {
+    var s = scenes[i];
+
+    /* visible */
+    if (!s.visible) continue;
+
+    /* fill */
+    e = this.fill(e, scenes, i);
+
+    /* image */
+    e = this.expect("image", e);
+    e.setAttribute("preserveAspectRatio", "none");
+    e.setAttribute("x", s.left);
+    e.setAttribute("y", s.top);
+    e.setAttribute("width", s.width);
+    e.setAttribute("height", s.height);
+    e.setAttribute("cursor", s.cursor);
+    e.setAttributeNS(pv.ns.xlink, "href", s.url);
+    e = this.append(e, scenes, i);
+
+    /* stroke */
+    e = this.stroke(e, scenes, i);
+  }
+  return e;
+};
+pv.SvgScene.label = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0; i < scenes.length; i++) {
+    var s = scenes[i];
+
+    /* visible */
+    if (!s.visible) continue;
+    var fill = pv.color(s.textStyle);
+    if (!fill.opacity) continue;
+
+    /* text-baseline, text-align */
+    var x = 0, y = 0, dy = 0, anchor = "start";
+    switch (s.textBaseline) {
+      case "middle": dy = ".35em"; break;
+      case "top": dy = ".71em"; y = s.textMargin; break;
+      case "bottom": y = "-" + s.textMargin; break;
+    }
+    switch (s.textAlign) {
+      case "right": anchor = "end"; x = "-" + s.textMargin; break;
+      case "center": anchor = "middle"; break;
+      case "left": x = s.textMargin; break;
+    }
+
+    e = this.expect("text", e);
+    e.setAttribute("pointer-events", "none");
+    e.setAttribute("x", x);
+    e.setAttribute("y", y);
+    e.setAttribute("dy", dy);
+    e.setAttribute("text-anchor", anchor);
+    e.setAttribute("transform",
+        "translate(" + s.left + "," + s.top + ")"
+        + (s.textAngle ? " rotate(" + 180 * s.textAngle / Math.PI + ")" : ""));
+    e.setAttribute("fill", fill.color);
+    e.setAttribute("fill-opacity", fill.opacity);
+    e.style.font = s.font;
+    e.style.textShadow = s.textShadow;
+    if (e.firstChild) e.firstChild.nodeValue = s.text;
+    else e.appendChild(document.createTextNode(s.text));
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+// TODO fillStyle for lineSegment?
+// TODO lineOffset for flow maps?
+
+pv.SvgScene.line = function(scenes) {
+  var e = scenes.$g.firstChild;
+  if (scenes.length < 2) return e;
+  var s = scenes[0];
+
+  /* segmented */
+  if (s.segmented) return this.lineSegment(scenes);
+
+  /* visible */
+  if (!s.visible) return e;
+  var fill = pv.color(s.fillStyle), stroke = pv.color(s.strokeStyle);
+  if (!fill.opacity && !stroke.opacity) return e;
+
+  /* points */
+  var p = "";
+  for (var i = 0; i < scenes.length; i++) {
+    var si = scenes[i];
+    p += si.left + "," + si.top + " ";
+
+    /* interpolate (assume linear by default) */
+    if (i < scenes.length - 1) {
+      var sj = scenes[i + 1];
+      switch (s.interpolate) {
+        case "step-before": {
+          p += si.left + "," + sj.top + " ";
+          break;
+        }
+        case "step-after": {
+          p += sj.left + "," + si.top + " ";
+          break;
+        }
+      }
+    }
+  }
+
+
+  e = this.expect("polyline", e);
+  e.setAttribute("cursor", s.cursor);
+  e.setAttribute("points", p);
+  e.setAttribute("fill", fill.color);
+  e.setAttribute("fill-opacity", fill.opacity);
+  e.setAttribute("stroke", stroke.color);
+  e.setAttribute("stroke-opacity", stroke.opacity);
+  e.setAttribute("stroke-width", s.lineWidth);
+  return this.append(e, scenes, 0);
+};
+
+pv.SvgScene.lineSegment = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0, n = scenes.length - 1; i < n; i++) {
+    var s1 = scenes[i], s2 = scenes[i + 1];
+
+    /* visible */
+    if (!s1.visible || !s2.visible) continue;
+    var stroke = pv.color(s1.strokeStyle);
+    if (!stroke.opacity) continue;
+
+    /* Line-line intersection, per Akenine-Moller 16.16.1. */
+    function intersect(o1, d1, o2, d2) {
+      return o1.plus(d1.times(o2.minus(o1).dot(d2.perp()) / d1.dot(d2.perp())));
+    }
+
+    /*
+     * P1-P2 is the current line segment. V is a vector that is perpendicular to
+     * the line segment, and has length lineWidth / 2. ABCD forms the initial
+     * bounding box of the line segment (i.e., the line segment if we were to do
+     * no joins).
+     */
+    var p1 = pv.vector(s1.left, s1.top),
+        p2 = pv.vector(s2.left, s2.top),
+        p = p2.minus(p1),
+        v = p.perp().norm(),
+        w = v.times(s1.lineWidth / 2),
+        a = p1.plus(w),
+        b = p2.plus(w),
+        c = p2.minus(w),
+        d = p1.minus(w);
+
+    /*
+     * Start join. P0 is the previous line segment's start point. We define the
+     * cutting plane as the average of the vector perpendicular to P0-P1, and
+     * the vector perpendicular to P1-P2. This insures that the cross-section of
+     * the line on the cutting plane is equal if the line-width is unchanged.
+     * Note that we don't implement miter limits, so these can get wild.
+     */
+    if (i > 0) {
+      var s0 = scenes[i - 1];
+      if (s0.visible) {
+        var v1 = p1.minus(s0.left, s0.top).perp().norm().plus(v);
+        d = intersect(p1, v1, d, p);
+        a = intersect(p1, v1, a, p);
+      }
+    }
+
+    /* Similarly, for end join. */
+    if (i < (n - 1)) {
+      var s3 = scenes[i + 2];
+      if (s3.visible) {
+        var v2 = pv.vector(s3.left, s3.top).minus(p2).perp().norm().plus(v);
+        c = intersect(p2, v2, c, p);
+        b = intersect(p2, v2, b, p);
+      }
+    }
+
+    /* points */
+    var p = a.x + "," + a.y + " "
+      + b.x + "," + b.y + " "
+      + c.x + "," + c.y + " "
+      + d.x + "," + d.y;
+
+    e = this.expect("polygon", e);
+    e.setAttribute("cursor", s1.cursor);
+    e.setAttribute("points", p);
+    e.setAttribute("fill", stroke.color);
+    e.setAttribute("fill-opacity", stroke.opacity);
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+var guid = 0;
+
+pv.SvgScene.panel = function(scenes) {
+  var g = scenes.$g, e = g && g.firstChild;
+  for (var i = 0; i < scenes.length; i++) {
+    var s = scenes[i];
+
+    /* visible */
+    if (!s.visible) continue;
+
+    /* svg */
+    if (!scenes.parent) {
+      s.canvas.style.display = "inline-block";
+      g = s.canvas.firstChild;
+      if (!g) {
+        g = s.canvas.appendChild(this.create("svg"));
+        g.onclick
+            = g.onmousedown
+            = g.onmouseup
+            = g.onmousemove
+            = g.onmouseout
+            = g.onmouseover
+            = pv.SvgScene.dispatch;
+      }
+      scenes.$g = g;
+      g.setAttribute("width", s.width + s.left + s.right);
+      g.setAttribute("height", s.height + s.top + s.bottom);
+      if (typeof e == "undefined") e = g.firstChild;
+    }
+
+    /* clip (nest children) */
+    if (s.overflow == "hidden") {
+      var c = this.expect("g", e), id = (guid++).toString(36);
+      c.setAttribute("clip-path", "url(#" + id + ")");
+      if (!c.parentNode) g.appendChild(c);
+      scenes.$g = g = c;
+      e = c.firstChild;
+
+      e = this.expect("clipPath", e);
+      e.setAttribute("id", id);
+      var r = e.firstChild ||  e.appendChild(this.create("rect"));
+      r.setAttribute("x", s.left);
+      r.setAttribute("y", s.top);
+      r.setAttribute("width", s.width);
+      r.setAttribute("height", s.height);
+      if (!e.parentNode) g.appendChild(e);
+      e = e.nextSibling;
+    }
+
+    /* fill */
+    e = this.fill(e, scenes, i);
+
+    /* children */
+    for (var j = 0; j < s.children.length; j++) {
+      s.children[j].$g = e = this.expect("g", e);
+      e.setAttribute("transform", "translate(" + s.left + "," + s.top + ")");
+      this.updateAll(s.children[j]);
+      if (!e.parentNode) g.appendChild(e);
+      e = e.nextSibling;
+    }
+
+    /* stroke */
+    e = this.stroke(e, scenes, i);
+
+    /* clip (restore group) */
+    if (s.overflow == "hidden") {
+      scenes.$g = g = c.parentNode;
+      e = c.nextSibling;
+    }
+  }
+  return e;
+};
+
+pv.SvgScene.fill = function(e, scenes, i) {
+  var s = scenes[i], fill = pv.color(s.fillStyle);
+  if (fill.opacity) {
+    e = this.expect("rect", e);
+    e.setAttribute("x", s.left);
+    e.setAttribute("y", s.top);
+    e.setAttribute("width", s.width);
+    e.setAttribute("height", s.height);
+    e.setAttribute("cursor", s.cursor);
+    e.setAttribute("fill", fill.color);
+    e.setAttribute("fill-opacity", fill.opacity);
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+
+pv.SvgScene.stroke = function(e, scenes, i) {
+  var s = scenes[i], stroke = pv.color(s.strokeStyle);
+  if (stroke.opacity) {
+    e = this.expect("rect", e);
+    e.setAttribute("x", s.left);
+    e.setAttribute("y", s.top);
+    e.setAttribute("width", Math.max(1E-10, s.width));
+    e.setAttribute("height", Math.max(1E-10, s.height));
+    e.setAttribute("cursor", s.cursor);
+    e.setAttribute("fill", "none");
+    e.setAttribute("stroke", stroke.color);
+    e.setAttribute("stroke-opacity", stroke.opacity);
+    e.setAttribute("stroke-width", s.lineWidth);
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+pv.SvgScene.rule = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0; i < scenes.length; i++) {
+    var s = scenes[i];
+
+    /* visible */
+    if (!s.visible) continue;
+    var stroke = pv.color(s.strokeStyle);
+    if (!stroke.opacity) continue;
+
+    e = this.expect("line", e);
+    e.setAttribute("cursor", s.cursor);
+    e.setAttribute("x1", s.left);
+    e.setAttribute("y1", s.top);
+    e.setAttribute("x2", s.left + s.width);
+    e.setAttribute("y2", s.top + s.height);
+    e.setAttribute("stroke", stroke.color);
+    e.setAttribute("stroke-opacity", stroke.opacity);
+    e.setAttribute("stroke-width", s.lineWidth);
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+pv.SvgScene.wedge = function(scenes) {
+  var e = scenes.$g.firstChild;
+  for (var i = 0; i < scenes.length; i++) {
+    var s = scenes[i];
+
+    /* visible */
+    if (!s.visible) continue;
+    var fill = pv.color(s.fillStyle), stroke = pv.color(s.strokeStyle);
+    if (!fill.opacity && !stroke.opacity) continue;
+
+    /* points */
+    var r1 = s.innerRadius, r2 = s.outerRadius, a = Math.abs(s.angle), p;
+    if (a >= 2 * Math.PI) {
+      if (r1) {
+        p = "M0," + r2
+            + "A" + r2 + "," + r2 + " 0 1,1 0," + (-r2)
+            + "A" + r2 + "," + r2 + " 0 1,1 0," + r2
+            + "M0," + r1
+            + "A" + r1 + "," + r1 + " 0 1,1 0," + (-r1)
+            + "A" + r1 + "," + r1 + " 0 1,1 0," + r1
+            + "Z";
+      } else {
+        p = "M0," + r2
+            + "A" + r2 + "," + r2 + " 0 1,1 0," + (-r2)
+            + "A" + r2 + "," + r2 + " 0 1,1 0," + r2
+            + "Z";
+      }
+    } else {
+      var sa = Math.min(s.startAngle, s.endAngle),
+          ea = Math.max(s.startAngle, s.endAngle),
+          c1 = Math.cos(sa), c2 = Math.cos(ea),
+          s1 = Math.sin(sa), s2 = Math.sin(ea);
+      if (r1) {
+        p = "M" + r2 * c1 + "," + r2 * s1
+            + "A" + r2 + "," + r2 + " 0 "
+            + ((a < Math.PI) ? "0" : "1") + ",1 "
+            + r2 * c2 + "," + r2 * s2
+            + "L" + r1 * c2 + "," + r1 * s2
+            + "A" + r1 + "," + r1 + " 0 "
+            + ((a < Math.PI) ? "0" : "1") + ",0 "
+            + r1 * c1 + "," + r1 * s1 + "Z";
+      } else {
+        p = "M" + r2 * c1 + "," + r2 * s1
+            + "A" + r2 + "," + r2 + " 0 "
+            + ((a < Math.PI) ? "0" : "1") + ",1 "
+            + r2 * c2 + "," + r2 * s2 + "L0,0Z";
+      }
+    }
+
+    e = this.expect("path", e);
+    e.setAttribute("fill-rule", "evenodd");
+    e.setAttribute("cursor", s.cursor);
+    e.setAttribute("transform", "translate(" + s.left + "," + s.top + ")");
+    e.setAttribute("d", p);
+    e.setAttribute("fill", fill.color);
+    e.setAttribute("fill-opacity", fill.opacity);
+    e.setAttribute("stroke", stroke.color);
+    e.setAttribute("stroke-opacity", stroke.opacity);
+    e.setAttribute("stroke-width", s.lineWidth);
+    e = this.append(e, scenes, i);
+  }
+  return e;
+};
+/**
+ * Constructs a new mark with default properties. Marks, with the exception of
+ * the root panel, are not typically constructed directly; instead, they are
+ * added to a panel or an existing mark via {@link pv.Mark#add}.
+ *
+ * @class Represents a data-driven graphical mark. The <tt>Mark</tt> class is
+ * the base class for all graphical marks in Protovis; it does not provide any
+ * specific rendering functionality, but together with {@link Panel} establishes
+ * the core framework.
+ *
+ * <p>Concrete mark types include familiar visual elements such as bars, lines
+ * and labels. Although a bar mark may be used to construct a bar chart, marks
+ * know nothing about charts; it is only through their specification and
+ * composition that charts are produced. These building blocks permit many
+ * combinatorial possibilities.
+ *
+ * <p>Marks are associated with <b>data</b>: a mark is generated once per
+ * associated datum, mapping the datum to visual <b>properties</b> such as
+ * position and color. Thus, a single mark specification represents a set of
+ * visual elements that share the same data and visual encoding. The type of
+ * mark defines the names of properties and their meaning. A property may be
+ * static, ignoring the associated datum and returning a constant; or, it may be
+ * dynamic, derived from the associated datum or index. Such dynamic encodings
+ * can be specified succinctly using anonymous functions. Special properties
+ * called event handlers can be registered to add interactivity.
+ *
+ * <p>Protovis uses <b>inheritance</b> to simplify the specification of related
+ * marks: a new mark can be derived from an existing mark, inheriting its
+ * properties. The new mark can then override properties to specify new
+ * behavior, potentially in terms of the old behavior. In this way, the old mark
+ * serves as the <b>prototype</b> for the new mark. Most mark types share the
+ * same basic properties for consistency and to facilitate inheritance.
+ *
+ * <p>The prioritization of redundant properties is as follows:<ol>
+ *
+ * <li>If the <tt>width</tt> property is not specified (i.e., null), its value
+ * is the width of the parent panel, minus this mark's left and right margins;
+ * the left and right margins are zero if not specified.
+ *
+ * <li>Otherwise, if the <tt>right</tt> margin is not specified, its value is
+ * the width of the parent panel, minus this mark's width and left margin; the
+ * left margin is zero if not specified.
+ *
+ * <li>Otherwise, if the <tt>left</tt> property is not specified, its value is
+ * the width of the parent panel, minus this mark's width and the right margin.
+ *
+ * </ol>This prioritization is then duplicated for the <tt>height</tt>,
+ * <tt>bottom</tt> and <tt>top</tt> properties, respectively.
+ *
+ * <p>While most properties are <i>variable</i>, some mark types, such as lines
+ * and areas, generate a single visual element rather than a distinct visual
+ * element per datum. With these marks, some properties may be <b>fixed</b>.
+ * Fixed properties can vary per mark, but not <i>per datum</i>! These
+ * properties are evaluated solely for the first (0-index) datum, and typically
+ * are specified as a constant. However, it is valid to use a function if the
+ * property varies between panels or is dynamically generated.
+ *
+ * <p>See also the <a href="../../api/">Protovis guide</a>.
+ */
+pv.Mark = function() {
+  /*
+   * TYPE 0 constant defs
+   * TYPE 1 function defs
+   * TYPE 2 constant properties
+   * TYPE 3 function properties
+   * in order of evaluation!
+   */
+  this.$properties = [];
+};
+
+/** @private TOOD */
+pv.Mark.prototype.properties = {};
+
+/**
+ * @private Defines and registers a property method for the property with the
+ * given name.  This method should be called on a mark class prototype to define
+ * each exposed property. (Note this refers to the JavaScript
+ * <tt>prototype</tt>, not the Protovis mark prototype, which is the {@link
+ * #proto} field.)
+ *
+ * <p>The created property method supports several modes of invocation: <ol>
+ *
+ * <li>If invoked with a <tt>Function</tt> argument, this function is evaluated
+ * for each associated datum. The return value of the function is used as the
+ * computed property value. The context of the function (<tt>this</tt>) is this
+ * mark. The arguments to the function are the associated data of this mark and
+ * any enclosing panels. For example, a linear encoding of numerical data to
+ * height is specified as
+ *
+ * <pre>m.height(function(d) d * 100);</pre>
+ *
+ * The expression <tt>d * 100</tt> will be evaluated for the height property of
+ * each mark instance. The return value of the property method (e.g.,
+ * <tt>m.height</tt>) is this mark (<tt>m</tt>)).<p>
+ *
+ * <li>If invoked with a non-function argument, the property is treated as a
+ * constant. The return value of the property method (e.g., <tt>m.height</tt>)
+ * is this mark.<p>
+ *
+ * <li>If invoked with no arguments, the computed property value for the current
+ * mark instance in the scene graph is returned. This facilitates <i>property
+ * chaining</i>, where one mark's properties are defined in terms of another's.
+ * For example, to offset a mark's location from its prototype, you might say
+ *
+ * <pre>m.top(function() this.proto.top() + 10);</pre>
+ *
+ * Note that the index of the mark being evaluated (in the above example,
+ * <tt>this.proto</tt>) is inherited from the <tt>Mark</tt> class and set by
+ * this mark. So, if the fifth element's top property is being evaluated, the
+ * fifth instance of <tt>this.proto</tt> will similarly be queried for the value
+ * of its top property. If the mark being evaluated has a different number of
+ * instances, or its data is unrelated, the behavior of this method is
+ * undefined. In these cases it may be better to index the <tt>scene</tt>
+ * explicitly to specify the exact instance.
+ *
+ * </ol><p>Property names should follow standard JavaScript method naming
+ * conventions, using lowerCamel-style capitalization.
+ *
+ * <p>In addition to creating the property method, every property is registered
+ * in the {@link #properties} map on the <tt>prototype</tt>. Although this is an
+ * instance field, it is considered immutable and shared by all instances of a
+ * given mark type. The <tt>properties</tt> map can be queried to see if a mark
+ * type defines a particular property, such as width or height.
+ *
+ * @param {string} name the property name.
+ */
+pv.Mark.prototype.property = function(name) {
+  if (!this.hasOwnProperty("properties")) {
+    this.properties = pv.extend(this.properties);
+  }
+  this.properties[name] = true;
+
+  /*
+   * Define the setter-getter globally, since the default behavior should be the
+   * same for all properties, and since the Protovis inheritance chain is
+   * independent of the JavaScript inheritance chain. For example, anchors
+   * define a "name" property that is evaluated on derived marks, even though
+   * those marks don't normally have a name.
+   */
+  pv.Mark.prototype[name] = function(v) {
+      if (arguments.length) {
+        this.$properties.push({
+            name: name,
+            type: (typeof v == "function") ? 3 : 2,
+            value: v
+          });
+        return this;
+      }
+      return this.scene[this.index][name];
+    };
+
+  return this;
+};
+
+/* Define all global properties. */
+pv.Mark.prototype
+    .property("data")
+    .property("visible")
+    .property("left")
+    .property("right")
+    .property("top")
+    .property("bottom")
+    .property("cursor")
+    .property("title")
+    .property("reverse");
+
+/**
+ * The mark type; a lower camelCase name. The type name controls rendering
+ * behavior, and unless the rendering engine is extended, must be one of the
+ * built-in concrete mark types: area, bar, dot, image, label, line, panel,
+ * rule, or wedge.
+ *
+ * @type string
+ * @name pv.Mark.prototype.type
+ */
+
+/**
+ * The mark prototype, possibly undefined, from which to inherit property
+ * functions. The mark prototype is not necessarily of the same type as this
+ * mark. Any properties defined on this mark will override properties inherited
+ * either from the prototype or from the type-specific defaults.
+ *
+ * @type pv.Mark
+ * @name pv.Mark.prototype.proto
+ */
+
+/**
+ * The enclosing parent panel. The parent panel is generally undefined only for
+ * the root panel; however, it is possible to create "offscreen" marks that are
+ * used only for inheritance purposes.
+ *
+ * @type pv.Panel
+ * @name pv.Mark.prototype.parent
+ */
+
+/**
+ * The child index. -1 if the enclosing parent panel is null; otherwise, the
+ * zero-based index of this mark into the parent panel's <tt>children</tt> array.
+ *
+ * @type number
+ */
+pv.Mark.prototype.childIndex = -1;
+
+/**
+ * The mark index. The value of this field depends on which instance (i.e.,
+ * which element of the data array) is currently being evaluated. During the
+ * build phase, the index is incremented over each datum; when handling events,
+ * the index is set to the instance that triggered the event.
+ *
+ * @type number
+ */
+pv.Mark.prototype.index = -1;
+
+/**
+ * The scene graph. The scene graph is an array of objects; each object (or
+ * "node") corresponds to an instance of this mark and an element in the data
+ * array. The scene graph can be traversed to lookup previously-evaluated
+ * properties.
+ *
+ * <p>For instance, consider a stacked area chart. The bottom property of the
+ * area can be defined using the <i>cousin</i> instance, which is the current
+ * area instance in the previous instantiation of the parent panel. In this
+ * sample code,
+ *
+ * <pre>new pv.Panel()
+ *     .width(150).height(150)
+ *   .add(pv.Panel)
+ *     .data([[1, 1.2, 1.7, 1.5, 1.7],
+ *            [.5, 1, .8, 1.1, 1.3],
+ *            [.2, .5, .8, .9, 1]])
+ *   .add(pv.Area)
+ *     .data(function(d) d)
+ *     .bottom(function() {
+ *         var c = this.cousin();
+ *         return c ? (c.bottom + c.height) : 0;
+ *       })
+ *     .height(function(d) d * 40)
+ *     .left(function() this.index * 35)
+ *   .root.render();</pre>
+ *
+ * the bottom property is computed based on the upper edge of the corresponding
+ * datum in the previous series. The area's parent panel is instantiated once
+ * per series, so the cousin refers to the previous (below) area mark. (Note
+ * that the position of the upper edge is not the same as the top property,
+ * which refers to the top margin: the distance from the top edge of the panel
+ * to the top edge of the mark.)
+ *
+ * @see #first
+ * @see #last
+ * @see #sibling
+ * @see #cousin
+ * @name pv.Mark.prototype.scene
+ */
+
+/**
+ * The root parent panel. This may be undefined for "offscreen" marks that are
+ * created for inheritance purposes only.
+ *
+ * @type pv.Panel
+ * @name pv.Mark.prototype.root
+ */
+
+/**
+ * The data property; an array of objects. The size of the array determines the
+ * number of marks that will be instantiated; each element in the array will be
+ * passed to property functions to compute the property values. Typically, the
+ * data property is specified as a constant array, such as
+ *
+ * <pre>m.data([1, 2, 3, 4, 5]);</pre>
+ *
+ * However, it is perfectly acceptable to define the data property as a
+ * function. This function might compute the data dynamically, allowing
+ * different data to be used per enclosing panel. For instance, in the stacked
+ * area graph example (see {@link #scene}), the data function on the area mark
+ * dereferences each series.
+ *
+ * @type array
+ * @name pv.Mark.prototype.data
+ */
+
+/**
+ * The visible property; a boolean determining whether or not the mark instance
+ * is visible. If a mark instance is not visible, its other properties will not
+ * be evaluated. Similarly, for panels no child marks will be rendered.
+ *
+ * @type boolean
+ * @name pv.Mark.prototype.visible
+ */
+
+/**
+ * The left margin; the distance, in pixels, between the left edge of the
+ * enclosing panel and the left edge of this mark. Note that in some cases this
+ * property may be redundant with the right property, or with the conjunction of
+ * right and width.
+ *
+ * @type number
+ * @name pv.Mark.prototype.left
+ */
+
+/**
+ * The right margin; the distance, in pixels, between the right edge of the
+ * enclosing panel and the right edge of this mark. Note that in some cases this
+ * property may be redundant with the left property, or with the conjunction of
+ * left and width.
+ *
+ * @type number
+ * @name pv.Mark.prototype.right
+ */
+
+/**
+ * The top margin; the distance, in pixels, between the top edge of the
+ * enclosing panel and the top edge of this mark. Note that in some cases this
+ * property may be redundant with the bottom property, or with the conjunction
+ * of bottom and height.
+ *
+ * @type number
+ * @name pv.Mark.prototype.top
+ */
+
+/**
+ * The bottom margin; the distance, in pixels, between the bottom edge of the
+ * enclosing panel and the bottom edge of this mark. Note that in some cases
+ * this property may be redundant with the top property, or with the conjunction
+ * of top and height.
+ *
+ * @type number
+ * @name pv.Mark.prototype.bottom
+ */
+
+/**
+ * The cursor property; corresponds to the CSS cursor property. This is
+ * typically used in conjunction with event handlers to indicate interactivity.
+ *
+ * @type string
+ * @name pv.Mark.prototype.cursor
+ * @see <a href="http://www.w3.org/TR/CSS2/ui.html#propdef-cursor">CSS2 cursor</a>
+ */
+
+/**
+ * The title property; corresponds to the HTML/SVG title property, allowing the
+ * general of simple plain text tooltips.
+ *
+ * @type string
+ * @name pv.Mark.prototype.title
+ */
+
+/**
+ * The reverse property; a boolean determining whether marks are ordered from
+ * front-to-back or back-to-front. SVG does not support explicit z-ordering;
+ * shapes are rendered in the order they appear. Thus, by default, marks are
+ * rendered in data order. Setting the reverse property to false reverses the
+ * order in which they are rendered; however, the properties are still evaluated
+ * (i.e., built) in forward order.
+ *
+ * @type boolean
+ * @name pv.Mark.prototype.reverse
+ */
+
+/**
+ * Default properties for all mark types. By default, the data array is the
+ * parent data as a single-element array; if the data property is not specified,
+ * this causes each mark to be instantiated as a singleton with the parents
+ * datum. The visible property is true by default, and the reverse property is
+ * false.
+ *
+ * @type pv.Mark
+ */
+pv.Mark.prototype.defaults = new pv.Mark()
+    .data(function(d) { return [d]; })
+    .visible(true)
+    .reverse(false)
+    .cursor("")
+    .title("");
+
+/* Private categorical colors for default fill & stroke styles. */
+var defaultFillStyle = pv.Colors.category20().by(pv.parent),
+    defaultStrokeStyle = pv.Colors.category10().by(pv.parent);
+
+/**
+ * Sets the prototype of this mark to the specified mark. Any properties not
+ * defined on this mark may be inherited from the specified prototype mark, or
+ * its prototype, and so on. The prototype mark need not be the same type of
+ * mark as this mark. (Note that for inheritance to be useful, properties with
+ * the same name on different mark types should have equivalent meaning.)
+ *
+ * @param {pv.Mark} proto the new prototype.
+ * @return {pv.Mark} this mark.
+ * @see #add
+ */
+pv.Mark.prototype.extend = function(proto) {
+  this.proto = proto;
+  return this;
+};
+
+/**
+ * Adds a new mark of the specified type to the enclosing parent panel, whilst
+ * simultaneously setting the prototype of the new mark to be this mark.
+ *
+ * @param {function} type the type of mark to add; a constructor, such as
+ * <tt>pv.Bar</tt>.
+ * @return {pv.Mark} the new mark.
+ * @see #extend
+ */
+pv.Mark.prototype.add = function(type) {
+  return this.parent.add(type).extend(this);
+};
+
+/**
+ * Defines a local variable on this mark. Local variables are initialized once
+ * per mark (i.e., per parent panel instance), and can be used to store local
+ * state for the mark. Here are a few reasons you might want to use
+ * <tt>def</tt>:
+ *
+ * <p>1. To store local state. For example, say you were visualizing employment
+ * statistics, and your root panel had an array of occupations. In a child
+ * panel, you might want to initialize a local scale, and reference it from a
+ * property function:
+ *
+ * <pre>.def("y", function(d) pv.Scale.linear(0, pv.max(d.values)).range(0, h))
+ * .height(function(d) this.y()(d))</pre>
+ *
+ * In this example, <tt>this.y()</tt> returns the defined local scale. We then
+ * invoke the scale function, passing in the datum, to compute the height.  Note
+ * that defs are similar to fixed properties: they are only evaluated once per
+ * parent panel, and <tt>this.y()</tt> returns a function, rather than
+ * automatically evaluating this function as a property.
+ *
+ * <p>2. To store temporary state for interaction. Say you have an array of
+ * bars, and you want to color the bar differently if the mouse is over it. Use
+ * <tt>def</tt> to define a local variable, and event handlers to override this
+ * variable interactively:
+ *
+ * <pre>.def("i", -1)
+ * .event("mouseover", function() this.i(this.index))
+ * .event("mouseout", function() this.i(-1))
+ * .fillStyle(function() this.i() == this.index ? "red" : "blue")</pre>
+ *
+ * Notice that <tt>this.i()</tt> can be used both to set the value of <i>i</i>
+ * (when an argument is specified), and to get the value of <i>i</i> (when no
+ * arguments are specified). In this way, it's like other property methods.
+ *
+ * <p>3. To specify fixed properties efficiently. Sometimes, the value of a
+ * property may be locally a constant, but dependent on parent panel data which
+ * is variable. In this scenario, you can use <tt>def</tt> to define a property;
+ * it will only get computed once per mark, rather than once per datum.
+ *
+ * @param {string} name the name of the local variable.
+ * @param {function} [value] an optional initializer; may be a constant or a
+ * function.
+ */
+pv.Mark.prototype.def = function(name, value) {
+  this.$properties.push({
+      name: name,
+      type: (typeof value == "function") ? 1 : 0,
+      value: value
+    });
+  return this;
+};
+
+/**
+ * Returns an anchor with the specified name. While anchor names are typically
+ * constants, the anchor name is a true property, which means you can specify a
+ * function to compute the anchor name dynamically. See the
+ * {@link pv.Anchor#name} property for details.
+ *
+ * @param {string} name the anchor name; either a string or a property function.
+ * @returns {pv.Anchor} the new anchor.
+ */
+pv.Mark.prototype.anchor = function(name) {
+  var anchor = new pv.Anchor().extend(this).name(name);
+  anchor.parent = this.parent;
+  return anchor;
+};
+
+/**
+ * Returns the anchor target of this mark, if it is derived from an anchor;
+ * otherwise returns null. For example, if a label is derived from a bar anchor,
+ *
+ * <pre>bar.anchor("top").add(pv.Label);</pre>
+ *
+ * then property functions on the label can refer to the bar via the
+ * <tt>anchorTarget</tt> method. This method is also useful for mark types
+ * defining properties on custom anchors.
+ *
+ * @returns {pv.Mark} the anchor target of this mark; possibly null.
+ */
+pv.Mark.prototype.anchorTarget = function() {
+  var target = this;
+  while (!(target instanceof pv.Anchor)) {
+    target = target.proto;
+    if (!target) return null;
+  }
+  return target.proto;
+};
+
+/**
+ * Returns the first instance of this mark in the scene graph. This method can
+ * only be called when the mark is bound to the scene graph (for example, from
+ * an event handler, or within a property function).
+ *
+ * @returns a node in the scene graph.
+ */
+pv.Mark.prototype.first = function() {
+  return this.scene[0];
+};
+
+/**
+ * Returns the last instance of this mark in the scene graph. This method can
+ * only be called when the mark is bound to the scene graph (for example, from
+ * an event handler, or within a property function). In addition, note that mark
+ * instances are built sequentially, so the last instance of this mark may not
+ * yet be constructed.
+ *
+ * @returns a node in the scene graph.
+ */
+pv.Mark.prototype.last = function() {
+  return this.scene[this.scene.length - 1];
+};
+
+/**
+ * Returns the previous instance of this mark in the scene graph, or null if
+ * this is the first instance.
+ *
+ * @returns a node in the scene graph, or null.
+ */
+pv.Mark.prototype.sibling = function() {
+  return (this.index == 0) ? null : this.scene[this.index - 1];
+};
+
+/**
+ * Returns the current instance in the scene graph of this mark, in the previous
+ * instance of the enclosing parent panel. May return null if this instance
+ * could not be found. See the {@link pv.Layout.stack} function for an example
+ * property function using cousin.
+ *
+ * @see pv.Layout.stack
+ * @returns a node in the scene graph, or null.
+ */
+pv.Mark.prototype.cousin = function() {
+  var p = this.parent, s = p && p.sibling();
+  return (s && s.children) ? s.children[this.childIndex][this.index] : null;
+};
+
+/**
+ * Renders this mark, including recursively rendering all child marks if this is
+ * a panel.
+ */
+pv.Mark.prototype.render = function() {
+  /*
+   * Rendering consists of three phases: bind, build and update. The update
+   * phase is decoupled to allow different rendering engines.
+   *
+   * In the bind phase, inherited property definitions are cached so they do not
+   * need to be queried during build. In the build phase, properties are
+   * evaluated, and the scene graph is generated. In the update phase, the scene
+   * is rendered by creating and updating elements and attributes in the SVG
+   * image. No properties are evaluated during the update phase; instead the
+   * values computed previously in the build phase are simply translated into
+   * SVG.
+   */
+  this.bind();
+  this.build();
+  pv.Scene.updateAll(this.scene);
+};
+
+/** @private Computes the root data stack for the specified mark. */
+function argv(mark) {
+  var stack = [];
+  while (mark) {
+    stack.push(mark.scene[mark.index].data);
+    mark = mark.parent;
+  }
+  return stack;
+}
+
+/** @private TODO */
+pv.Mark.prototype.bind = function() {
+  var seen = {}, types = [[], [], [], []], data, visible;
+
+  /** TODO */
+  function bind(mark) {
+    do {
+      var properties = mark.$properties;
+      for (var i = properties.length - 1; i >= 0 ; i--) {
+        var p = properties[i];
+        if (!(p.name in seen)) {
+          seen[p.name] = 1;
+          switch (p.name) {
+            case "data": data = p; break;
+            case "visible": visible = p; break;
+            default: types[p.type].push(p); break;
+          }
+        }
+      }
+    } while (mark = mark.proto);
+  }
+
+  /** TODO */
+  function def(name) {
+    return function(v) {
+      var defs = this.scene.defs;
+      if (arguments.length) {
+        if (v == undefined) {
+          delete defs.locked[name];
+        } else {
+          defs.locked[name] = true;
+        }
+        defs.values[name] = v;
+        return this;
+      } else {
+        return defs.values[name];
+      }
+    };
+  }
+
+  /* Scan the proto chain for all defined properties. */
+  bind(this);
+  bind(this.defaults);
+  types[1].reverse();
+  types[3].reverse();
+
+  /* Any undefined properties are null. */
+  var mark = this;
+  do for (var name in mark.properties) {
+    if (!(name in seen)) {
+      seen[name] = 1;
+      types[2].push({name: name, type: 2, value: null});
+    }
+  } while (mark = mark.proto);
+
+  /* Define setter-getter for inherited defs. */
+  var defs = types[0].concat(types[1]);
+  for (var i = 0; i < defs.length; i++) {
+    var d = defs[i];
+    this[d.name] = def(d.name);
+  }
+
+  /* Setup binds to evaluate constants before functions. */
+  this.binds = {
+    data: data,
+    visible: visible,
+    defs: defs,
+    properties: pv.blend(types)
+  };
+};
+
+/**
+ * @private Evaluates properties and computes implied properties. Properties are
+ * stored in the {@link #scene} array for each instance of this mark.
+ *
+ * <p>As marks are built recursively, the {@link #index} property is updated to
+ * match the current index into the data array for each mark. Note that the
+ * index property is only set for the mark currently being built and its
+ * enclosing parent panels. The index property for other marks is unset, but is
+ * inherited from the global <tt>Mark</tt> class prototype. This allows mark
+ * properties to refer to properties on other marks <i>in the same panel</i>
+ * conveniently; however, in general it is better to reference mark instances
+ * specifically through the scene graph rather than depending on the magical
+ * behavior of {@link #index}.
+ *
+ * <p>The root scene array has a special property, <tt>data</tt>, which stores
+ * the current data stack. The first element in this stack is the current datum,
+ * followed by the datum of the enclosing parent panel, and so on. The data
+ * stack should not be accessed directly; instead, property functions are passed
+ * the current data stack as arguments.
+ *
+ * <p>The evaluation of the <tt>data</tt> and <tt>visible</tt> properties is
+ * special. The <tt>data</tt> property is evaluated first; unlike the other
+ * properties, the data stack is from the parent panel, rather than the current
+ * mark, since the data is not defined until the data property is evaluated.
+ * The <tt>visisble</tt> property is subsequently evaluated for each instance;
+ * only if true will the {@link #buildInstance} method be called, evaluating
+ * other properties and recursively building the scene graph.
+ *
+ * <p>If this mark is being re-built, any old instances of this mark that no
+ * longer exist (because the new data array contains fewer elements) will be
+ * cleared using {@link #clearInstance}.
+ *
+ * @param parent the instance of the parent panel from the scene graph.
+ */
+pv.Mark.prototype.build = function() {
+  var scene = this.scene;
+  if (!scene) {
+    scene = this.scene = [];
+    scene.mark = this;
+    scene.type = this.type;
+    scene.childIndex = this.childIndex;
+    if (this.parent) {
+      scene.parent = this.parent.scene;
+      scene.parentIndex = this.parent.index;
+    }
+  }
+
+  /* Set the data stack. */
+  var stack = this.root.scene.data;
+  if (!stack) this.root.scene.data = stack = argv(this.parent);
+
+  /* Evaluate defs. */
+  if (this.binds.defs.length) {
+    var defs = scene.defs;
+    if (!defs) scene.defs = defs = {values: {}, locked: {}};
+    for (var i = 0; i < this.binds.defs.length; i++) {
+      var d = this.binds.defs[i];
+      if (!(d.name in defs.locked)) {
+        var v = d.value;
+        if (d.type == 1) {
+          property = d.name;
+          v = v.apply(this, stack);
+        }
+        defs.values[d.name] = v;
+      }
+    }
+  }
+
+  /* Evaluate special data property. */
+  var data = this.binds.data;
+  switch (data.type) {
+    case 0: case 1: data = defs.values.data; break;
+    case 2: data = data.value; break;
+    case 3: {
+      property = "data";
+      data = data.value.apply(this, stack);
+      break;
+    }
+  }
+
+  /* Create, update and delete scene nodes. */
+  stack.unshift(null);
+  scene.length = data.length;
+  for (var i = 0; i < data.length; i++) {
+    pv.Mark.prototype.index = this.index = i;
+    var s = scene[i];
+    if (!s) scene[i] = s = {};
+    s.data = stack[0] = data[i];
+
+    /* Evaluate special visible property. */
+    var visible = this.binds.visible;
+    switch (visible.type) {
+      case 0: case 1: visible = defs.values.visible; break;
+      case 2: visible = visible.value; break;
+      case 3: {
+        property = "visible";
+        visible = visible.value.apply(this, stack);
+        break;
+      }
+    }
+
+    if (s.visible = visible) this.buildInstance(s);
+  }
+  stack.shift();
+  delete this.index;
+  pv.Mark.prototype.index = -1;
+  if (!this.parent) scene.data = null;
+
+  return this;
+};
+
+/**
+ * @private Evaluates the specified array of properties for the specified
+ * instance <tt>s</tt> in the scene graph.
+ *
+ * @param s a node in the scene graph; the instance of the mark to build.
+ * @param properties an array of properties.
+ */
+pv.Mark.prototype.buildProperties = function(s, properties) {
+  for (var i = 0, n = properties.length; i < n; i++) {
+    var p = properties[i], v = p.value;
+    switch (p.type) {
+      case 0: case 1: v = this.scene.defs.values[p.name]; break;
+      case 3: {
+        property = p.name;
+        v = v.apply(this, this.root.scene.data);
+        break;
+      }
+    }
+    s[p.name] = v;
+  }
+};
+
+/**
+ * @private Evaluates all of the properties for this mark for the specified
+ * instance <tt>s</tt> in the scene graph. The set of properties to evaluate is
+ * retrieved from the {@link #properties} array for this mark type (see {@link
+ * #type}).  After these properties are evaluated, any <b>implied</b> properties
+ * may be computed by the mark and set on the scene graph; see
+ * {@link #buildImplied}.
+ *
+ * <p>For panels, this method recursively builds the scene graph for all child
+ * marks as well. In general, this method should not need to be overridden by
+ * concrete mark types.
+ *
+ * @param s a node in the scene graph; the instance of the mark to build.
+ */
+pv.Mark.prototype.buildInstance = function(s) {
+  this.buildProperties(s, this.binds.properties);
+  this.buildImplied(s);
+};
+
+/**
+ * @private Computes the implied properties for this mark for the specified
+ * instance <tt>s</tt> in the scene graph. Implied properties are those with
+ * dependencies on multiple other properties; for example, the width property
+ * may be implied if the left and right properties are set. This method can be
+ * overridden by concrete mark types to define new implied properties, if
+ * necessary.
+ *
+ * @param s a node in the scene graph; the instance of the mark to build.
+ */
+pv.Mark.prototype.buildImplied = function(s) {
+  var l = s.left;
+  var r = s.right;
+  var t = s.top;
+  var b = s.bottom;
+
+  /* Assume width and height are zero if not supported by this mark type. */
+  var p = this.properties;
+  var w = p.width ? s.width : 0;
+  var h = p.height ? s.height : 0;
+
+  /* Compute implied width, right and left. */
+  var width = this.parent ? this.parent.width() : (w + l + r);
+  if (w == null) {
+    w = width - (r = r || 0) - (l = l || 0);
+  } else if (r == null) {
+    r = width - w - (l = l || 0);
+  } else if (l == null) {
+    l = width - w - (r = r || 0);
+  }
+
+  /* Compute implied height, bottom and top. */
+  var height = this.parent ? this.parent.height() : (h + t + b);
+  if (h == null) {
+    h = height - (t = t || 0) - (b = b || 0);
+  } else if (b == null) {
+    b = height - h - (t = t || 0);
+  } else if (t == null) {
+    t = height - h - (b = b || 0);
+  }
+
+  s.left = l;
+  s.right = r;
+  s.top = t;
+  s.bottom = b;
+
+  /* Only set width and height if they are supported by this mark type. */
+  if (p.width) s.width = w;
+  if (p.height) s.height = h;
+};
+
+/**
+ * @private The name of the property being evaluated, for so-called "smart"
+ * functions that change behavior depending on which property is being
+ * evaluated. This functionality is somewhat magical, so for now, this feature
+ * is not exposed outside the library.
+ *
+ * @type string
+ */
+var property;
+
+/** @private The current mouse location. */
+var pageX = 0, pageY = 0;
+pv.listen(window, "mousemove", function(e) { pageX = e.pageX; pageY = e.pageY; });
+
+/**
+ * Returns the current location of the mouse (cursor) relative to this mark's
+ * parent. The <i>x</i> coordinate corresponds to the left margin, while the
+ * <i>y</i> coordinate corresponds to the top margin.
+ *
+ * @returns {pv.Vector} the mouse location.
+ */
+pv.Mark.prototype.mouse = function() {
+  var x = 0, y = 0, mark = (this instanceof pv.Panel) ? this : this.parent;
+  do {
+    x += mark.left();
+    y += mark.top();
+  } while (mark = mark.parent);
+  var node = this.root.canvas();
+  do {
+    x += node.offsetLeft;
+    y += node.offsetTop;
+  } while (node = node.offsetParent);
+  return pv.vector(pageX - x, pageY - y);
+};
+
+/**
+ * Registers an event handler for the specified event type with this mark. When
+ * an event of the specified type is triggered, the specified handler will be
+ * invoked. The handler is invoked in a similar method to property functions:
+ * the context is <tt>this</tt> mark instance, and the arguments are the full
+ * data stack. Event handlers can use property methods to manipulate the display
+ * properties of the mark:
+ *
+ * <pre>m.event("click", function() this.fillStyle("red"));</pre>
+ *
+ * Alternatively, the external data can be manipulated and the visualization
+ * redrawn:
+ *
+ * <pre>m.event("click", function(d) {
+ *     data = all.filter(function(k) k.name == d);
+ *     vis.render();
+ *   });</pre>
+ *
+ * The return value of the event handler determines which mark gets re-rendered.
+ * Use defs ({@link #def}) to set temporary state from event handlers.
+ *
+ * <p>The complete set of event types is defined by SVG; see the reference
+ * below. The set of supported event types is:<ul>
+ *
+ * <li>click
+ * <li>mousedown
+ * <li>mouseup
+ * <li>mouseover
+ * <li>mousemove
+ * <li>mouseout
+ *
+ * </ul>Since Protovis does not specify any concept of focus, it does not
+ * support key events; these should be handled outside the visualization using
+ * standard JavaScript. In the future, support for interaction may be extended
+ * to support additional event types, particularly those most relevant to
+ * interactive visualization, such as selection.
+ *
+ * <p>TODO In the current implementation, event handlers are not inherited from
+ * prototype marks. They must be defined explicitly on each interactive mark. In
+ * addition, only one event handler for a given event type can be defined; when
+ * specifying multiple event handlers for the same type, only the last one will
+ * be used.
+ *
+ * @see <a href="http://www.w3.org/TR/SVGTiny12/interact.html#SVGEvents">SVG events</a>
+ * @param {string} type the event type.
+ * @param {function} handler the event handler.
+ * @returns {pv.Mark} this.
+ */
+pv.Mark.prototype.event = function(type, handler) {
+  if (!this.$handlers) this.$handlers = {};
+  this.$handlers[type] = handler;
+  return this;
+};
+
+/** @private TODO */
+pv.Mark.prototype.dispatch = function(type, scenes, index) {
+  var l = this.$handlers && this.$handlers[type];
+  if (!l) {
+    if (this.parent) {
+      this.parent.dispatch(type, scenes.parent, scenes.parentIndex);
+    }
+    return;
+  }
+  try {
+
+    /* Setup the scene stack. */
+    var mark = this;
+    do {
+      mark.index = index;
+      mark.scene = scenes;
+      index = scenes.parentIndex;
+      scenes = scenes.parent;
+    } while (mark = mark.parent);
+
+    /* Execute the event listener. */
+    try {
+      mark = l.apply(this, this.root.scene.data = argv(this));
+    } finally {
+      this.root.scene.data = null;
+    }
+
+    /* Update the display. TODO dirtying. */
+    if (mark instanceof pv.Mark) mark.render();
+
+  } finally {
+
+    /* Restore the scene stack. */
+    var mark = this;
+    do {
+      if (mark.parent) delete mark.scene;
+      delete mark.index;
+    } while (mark = mark.parent);
+  }
+};
+/**
+ * Constructs a new mark anchor with default properties.
+ *
+ * @class Represents an anchor on a given mark. An anchor is itself a mark, but
+ * without a visual representation. It serves only to provide useful default
+ * properties that can be inherited by other marks. Each type of mark can define
+ * any number of named anchors for convenience. If the concrete mark type does
+ * not define an anchor implementation specifically, one will be inherited from
+ * the mark's parent class.
+ *
+ * <p>For example, the bar mark provides anchors for its four sides: left,
+ * right, top and bottom. Adding a label to the top anchor of a bar,
+ *
+ * <pre>bar.anchor("top").add(pv.Label);</pre>
+ *
+ * will render a text label on the top edge of the bar; the top anchor defines
+ * the appropriate position properties (top and left), as well as text-rendering
+ * properties for convenience (textAlign and textBaseline).
+ *
+ * @extends pv.Mark
+ */
+pv.Anchor = function() {
+  pv.Mark.call(this);
+};
+
+pv.Anchor.prototype = pv.extend(pv.Mark)
+    .property("name");
+
+/**
+ * The anchor name. The set of supported anchor names is dependent on the
+ * concrete mark type; see the mark type for details. For example, bars support
+ * left, right, top and bottom anchors.
+ *
+ * <p>While anchor names are typically constants, the anchor name is a true
+ * property, which means you can specify a function to compute the anchor name
+ * dynamically. For instance, if you wanted to alternate top and bottom anchors,
+ * saying
+ *
+ * <pre>m.anchor(function() (this.index % 2) ? "top" : "bottom").add(pv.Dot);</pre>
+ *
+ * would have the desired effect.
+ *
+ * @type string
+ * @name pv.Anchor.prototype.name
+ */
+/**
+ * Constructs a new area mark with default properties. Areas are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents an area mark: the solid area between two series of
+ * connected line segments. Unsurprisingly, areas are used most frequently for
+ * area charts.
+ *
+ * <p>Just as a line represents a polyline, the <tt>Area</tt> mark type
+ * represents a <i>polygon</i>. However, an area is not an arbitrary polygon;
+ * vertices are paired either horizontally or vertically into parallel
+ * <i>spans</i>, and each span corresponds to an associated datum. Either the
+ * width or the height must be specified, but not both; this determines whether
+ * the area is horizontally-oriented or vertically-oriented.  Like lines, areas
+ * can be stroked and filled with arbitrary colors.
+ *
+ * <p>See also the <a href="../../api/Area.html">Area guide</a>.
+ *
+ * @extends pv.Mark
+ */
+pv.Area = function() {
+  pv.Mark.call(this);
+};
+
+pv.Area.prototype = pv.extend(pv.Mark)
+    .property("width")
+    .property("height")
+    .property("lineWidth")
+    .property("strokeStyle")
+    .property("fillStyle")
+    .property("segmented")
+    .property("interpolate");
+
+pv.Area.prototype.type = "area";
+
+/**
+ * The width of a given span, in pixels; used for horizontal spans. If the width
+ * is specified, the height property should be 0 (the default). Either the top
+ * or bottom property should be used to space the spans vertically, typically as
+ * a multiple of the index.
+ *
+ * @type number
+ * @name pv.Area.prototype.width
+ */
+
+/**
+ * The height of a given span, in pixels; used for vertical spans. If the height
+ * is specified, the width property should be 0 (the default). Either the left
+ * or right property should be used to space the spans horizontally, typically
+ * as a multiple of the index.
+ *
+ * @type number
+ * @name pv.Area.prototype.height
+ */
+
+/**
+ * The width of stroked lines, in pixels; used in conjunction with
+ * <tt>strokeStyle</tt> to stroke the perimeter of the area. Unlike the
+ * {@link Line} mark type, the entire perimeter is stroked, rather than just one
+ * edge. The default value of this property is 1.5, but since the default stroke
+ * style is null, area marks are not stroked by default.
+ *
+ * <p>This property is <i>fixed</i> for non-segmented areas. See
+ * {@link pv.Mark}.
+ *
+ * @type number
+ * @name pv.Area.prototype.lineWidth
+ */
+
+/**
+ * The style of stroked lines; used in conjunction with <tt>lineWidth</tt> to
+ * stroke the perimeter of the area. Unlike the {@link Line} mark type, the
+ * entire perimeter is stroked, rather than just one edge. The default value of
+ * this property is null, meaning areas are not stroked by default.
+ *
+ * <p>This property is <i>fixed</i> for non-segmented areas. See
+ * {@link pv.Mark}.
+ *
+ * @type string
+ * @name pv.Area.prototype.strokeStyle
+ * @see pv.color
+ */
+
+/**
+ * The area fill style; if non-null, the interior of the polygon forming the
+ * area is filled with the specified color. The default value of this property
+ * is a categorical color.
+ *
+ * <p>This property is <i>fixed</i> for non-segmented areas. See
+ * {@link pv.Mark}.
+ *
+ * @type string
+ * @name pv.Area.prototype.fillStyle
+ * @see pv.color
+ */
+
+/**
+ * Whether the area is segmented; whether variations in fill style, stroke
+ * style, and the other properties are treated as fixed. Rendering segmented
+ * areas is noticeably slower than non-segmented areas.
+ *
+ * <p>This property is <i>fixed</i>. See {@link pv.Mark}.
+ *
+ * @type boolean
+ * @name pv.Area.prototype.segmented
+ */
+
+/**
+ * How to interpolate between values. Linear interpolation ("linear") is the
+ * default, producing a straight line between points. For piecewise constant
+ * functions (i.e., step functions), either "step-before" or "step-after" can be
+ * specified.
+ *
+ * <p>Note: this property is currently supported only on non-segmented areas.
+ *
+ * <p>This property is <i>fixed</i>. See {@link pv.Mark}.
+ *
+ * @type string
+ * @name pv.Area.prototype.interpolate
+ */
+
+/**
+ * Default properties for areas. By default, there is no stroke and the fill
+ * style is a categorical color.
+ *
+ * @type pv.Area
+ */
+pv.Area.prototype.defaults = new pv.Area()
+    .extend(pv.Mark.prototype.defaults)
+    .lineWidth(1.5)
+    .fillStyle(defaultFillStyle)
+    .interpolate("linear");
+
+/**
+ * Constructs a new area anchor with default properties. Areas support five
+ * different anchors:<ul>
+ *
+ * <li>top
+ * <li>left
+ * <li>center
+ * <li>bottom
+ * <li>right
+ *
+ * </ul>In addition to positioning properties (left, right, top bottom), the
+ * anchors support text rendering properties (text-align, text-baseline). Text is
+ * rendered to appear inside the area polygon.
+ *
+ * <p>To facilitate stacking of areas, the anchors are defined in terms of their
+ * opposite edge. For example, the top anchor defines the bottom property, such
+ * that the area grows upwards; the bottom anchor instead defines the top
+ * property, such that the area grows downwards. Of course, in general it is
+ * more robust to use panels and the cousin accessor to define stacked area
+ * marks; see {@link pv.Mark#scene} for an example.
+ *
+ * @param {string} name the anchor name; either a string or a property function.
+ * @returns {pv.Anchor}
+ */
+pv.Area.prototype.anchor = function(name) {
+  var area = this;
+  return pv.Mark.prototype.anchor.call(this, name)
+    .left(function() {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return area.left() + area.width() / 2;
+          case "right": return area.left() + area.width();
+        }
+        return null;
+      })
+    .right(function() {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return area.right() + area.width() / 2;
+          case "left": return area.right() + area.width();
+        }
+        return null;
+      })
+    .top(function() {
+        switch (this.name()) {
+          case "left":
+          case "right":
+          case "center": return area.top() + area.height() / 2;
+          case "bottom": return area.top() + area.height();
+        }
+        return null;
+      })
+    .bottom(function() {
+        switch (this.name()) {
+          case "left":
+          case "right":
+          case "center": return area.bottom() + area.height() / 2;
+          case "top": return area.bottom() + area.height();
+        }
+        return null;
+      })
+    .textAlign(function() {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return "center";
+          case "right": return "right";
+        }
+        return "left";
+      })
+    .textBaseline(function() {
+        switch (this.name()) {
+          case "right":
+          case "left":
+          case "center": return "middle";
+          case "top": return "top";
+        }
+        return "bottom";
+      });
+};
+
+/**
+ * @private Overrides the default behavior of {@link pv.Mark.buildImplied} such
+ * that the width and height are set to zero if null.
+ *
+ * @param s a node in the scene graph; the instance of the mark to build.
+ */
+pv.Area.prototype.buildImplied = function(s) {
+  if (s.height == null) s.height = 0;
+  if (s.width == null) s.width = 0;
+  pv.Mark.prototype.buildImplied.call(this, s);
+};
+
+/** @private */
+var pv_Area_specials = {left:1, top:1, right:1, bottom:1, width:1, height:1, name:1};
+
+/** @private */
+pv.Area.prototype.bind = function() {
+  pv.Mark.prototype.bind.call(this);
+  var binds = this.binds,
+      properties = binds.properties,
+      specials = binds.specials = [];
+  for (var i = 0, n = properties.length; i < n; i++) {
+    var p = properties[i];
+    if (p.name in pv_Area_specials) specials.push(p);
+  }
+};
+
+/** @private */
+pv.Area.prototype.buildInstance = function(s) {
+  if (this.index && !this.scene[0].segmented) {
+    this.buildProperties(s, this.binds.specials);
+    this.buildImplied(s);
+  } else {
+    pv.Mark.prototype.buildInstance.call(this, s);
+  }
+};
+/**
+ * Constructs a new bar mark with default properties. Bars are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents a bar: an axis-aligned rectangle that can be stroked and
+ * filled. Bars are used for many chart types, including bar charts, histograms
+ * and Gantt charts. Bars can also be used as decorations, for example to draw a
+ * frame border around a panel; in fact, a panel is a special type (a subclass)
+ * of bar.
+ *
+ * <p>Bars can be positioned in several ways. Most commonly, one of the four
+ * corners is fixed using two margins, and then the width and height properties
+ * determine the extent of the bar relative to this fixed location. For example,
+ * using the bottom and left properties fixes the bottom-left corner; the width
+ * then extends to the right, while the height extends to the top. As an
+ * alternative to the four corners, a bar can be positioned exclusively using
+ * margins; this is convenient as an inset from the containing panel, for
+ * example. See {@link pv.Mark} for details on the prioritization of redundant
+ * positioning properties.
+ *
+ * <p>See also the <a href="../../api/Bar.html">Bar guide</a>.
+ *
+ * @extends pv.Mark
+ */
+pv.Bar = function() {
+  pv.Mark.call(this);
+};
+
+pv.Bar.prototype = pv.extend(pv.Mark)
+    .property("width")
+    .property("height")
+    .property("lineWidth")
+    .property("strokeStyle")
+    .property("fillStyle");
+
+pv.Bar.prototype.type = "bar";
+
+/**
+ * The width of the bar, in pixels. If the left position is specified, the bar
+ * extends rightward from the left edge; if the right position is specified, the
+ * bar extends leftward from the right edge.
+ *
+ * @type number
+ * @name pv.Bar.prototype.width
+ */
+
+/**
+ * The height of the bar, in pixels. If the bottom position is specified, the
+ * bar extends upward from the bottom edge; if the top position is specified,
+ * the bar extends downward from the top edge.
+ *
+ * @type number
+ * @name pv.Bar.prototype.height
+ */
+
+/**
+ * The width of stroked lines, in pixels; used in conjunction with
+ * <tt>strokeStyle</tt> to stroke the bar's border.
+ *
+ * @type number
+ * @name pv.Bar.prototype.lineWidth
+ */
+
+/**
+ * The style of stroked lines; used in conjunction with <tt>lineWidth</tt> to
+ * stroke the bar's border. The default value of this property is null, meaning
+ * bars are not stroked by default.
+ *
+ * @type string
+ * @name pv.Bar.prototype.strokeStyle
+ * @see pv.color
+ */
+
+/**
+ * The bar fill style; if non-null, the interior of the bar is filled with the
+ * specified color. The default value of this property is a categorical color.
+ *
+ * @type string
+ * @name pv.Bar.prototype.fillStyle
+ * @see pv.color
+ */
+
+/**
+ * Default properties for bars. By default, there is no stroke and the fill
+ * style is a categorical color.
+ *
+ * @type pv.Bar
+ */
+pv.Bar.prototype.defaults = new pv.Bar()
+    .extend(pv.Mark.prototype.defaults)
+    .lineWidth(1.5)
+    .fillStyle(defaultFillStyle);
+
+/**
+ * Constructs a new bar anchor with default properties. Bars support five
+ * different anchors:<ul>
+ *
+ * <li>top
+ * <li>left
+ * <li>center
+ * <li>bottom
+ * <li>right
+ *
+ * </ul>In addition to positioning properties (left, right, top bottom), the
+ * anchors support text rendering properties (text-align, text-baseline). Text
+ * is rendered to appear inside the bar.
+ *
+ * <p>To facilitate stacking of bars, the anchors are defined in terms of their
+ * opposite edge. For example, the top anchor defines the bottom property, such
+ * that the bar grows upwards; the bottom anchor instead defines the top
+ * property, such that the bar grows downwards. Of course, in general it is more
+ * robust to use panels and the cousin accessor to define stacked bars; see
+ * {@link pv.Mark#scene} for an example.
+ *
+ * <p>Bar anchors also "smartly" specify position properties based on whether
+ * the derived mark type supports the width and height properties. If the
+ * derived mark type does not support these properties (e.g., dots), the
+ * position will be centered on the corresponding edge. Otherwise (e.g., bars),
+ * the position will be in the opposite side.
+ *
+ * @param {string} name the anchor name; either a string or a property function.
+ * @returns {pv.Anchor}
+ */
+pv.Bar.prototype.anchor = function(name) {
+  var bar = this;
+  return pv.Mark.prototype.anchor.call(this, name)
+    .left(function() {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return bar.left() + (this.properties.width ? 0 : (bar.width() / 2));
+          case "right": return bar.left() + bar.width();
+        }
+        return null;
+      })
+    .right(function() {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return bar.right() + (this.properties.width ? 0 : (bar.width() / 2));
+          case "left": return bar.right() + bar.width();
+        }
+        return null;
+      })
+    .top(function() {
+        switch (this.name()) {
+          case "left":
+          case "right":
+          case "center": return bar.top() + (this.properties.height ? 0 : (bar.height() / 2));
+          case "bottom": return bar.top() + bar.height();
+        }
+        return null;
+      })
+    .bottom(function() {
+        switch (this.name()) {
+          case "left":
+          case "right":
+          case "center": return bar.bottom() + (this.properties.height ? 0 : (bar.height() / 2));
+          case "top": return bar.bottom() + bar.height();
+        }
+        return null;
+      })
+    .textAlign(function() {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return "center";
+          case "right": return "right";
+        }
+        return "left";
+      })
+    .textBaseline(function() {
+        switch (this.name()) {
+          case "right":
+          case "left":
+          case "center": return "middle";
+          case "top": return "top";
+        }
+        return "bottom";
+      });
+};
+/**
+ * Constructs a new dot mark with default properties. Dots are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents a dot; a dot is simply a sized glyph centered at a given
+ * point that can also be stroked and filled. The <tt>size</tt> property is
+ * proportional to the area of the rendered glyph to encourage meaningful visual
+ * encodings. Dots can visually encode up to eight dimensions of data, though
+ * this may be unwise due to integrality. See {@link pv.Mark} for details on the
+ * prioritization of redundant positioning properties.
+ *
+ * <p>See also the <a href="../../api/Dot.html">Dot guide</a>.
+ *
+ * @extends pv.Mark
+ */
+pv.Dot = function() {
+  pv.Mark.call(this);
+};
+
+pv.Dot.prototype = pv.extend(pv.Mark)
+    .property("size")
+    .property("shape")
+    .property("angle")
+    .property("lineWidth")
+    .property("strokeStyle")
+    .property("fillStyle");
+
+pv.Dot.prototype.type = "dot";
+
+/**
+ * The size of the dot, in square pixels. Square pixels are used such that the
+ * area of the dot is linearly proportional to the value of the size property,
+ * facilitating representative encodings.
+ *
+ * @see #radius
+ * @type number
+ * @name pv.Dot.prototype.size
+ */
+
+/**
+ * The shape name. Several shapes are supported:<ul>
+ *
+ * <li>cross
+ * <li>triangle
+ * <li>diamond
+ * <li>square
+ * <li>tick
+ * <li>circle
+ *
+ * </ul>These shapes can be further changed using the {@link #angle} property;
+ * for instance, a cross can be turned into a plus by rotating. Similarly, the
+ * tick, which is vertical by default, can be rotated horizontally. Note that
+ * some shapes (cross and tick) do not have interior areas, and thus do not
+ * support fill style meaningfully.
+ *
+ * <p>Note: it may be more natural to use the {@link pv.Rule} mark for
+ * horizontal and vertical ticks. The tick shape is only necessary if angled
+ * ticks are needed.
+ *
+ * @type string
+ * @name pv.Dot.prototype.shape
+ */
+
+/**
+ * The rotation angle, in radians. Used to rotate shapes, such as to turn a
+ * cross into a plus.
+ *
+ * @type number
+ * @name pv.Dot.prototype.angle
+ */
+
+/**
+ * The width of stroked lines, in pixels; used in conjunction with
+ * <tt>strokeStyle</tt> to stroke the dot's shape.
+ *
+ * @type number
+ * @name pv.Dot.prototype.lineWidth
+ */
+
+/**
+ * The style of stroked lines; used in conjunction with <tt>lineWidth</tt> to
+ * stroke the dot's shape. The default value of this property is a categorical
+ * color.
+ *
+ * @type string
+ * @name pv.Dot.prototype.strokeStyle
+ * @see pv.color
+ */
+
+/**
+ * The fill style; if non-null, the interior of the dot is filled with the
+ * specified color. The default value of this property is null, meaning dots are
+ * not filled by default.
+ *
+ * @type string
+ * @name pv.Dot.prototype.fillStyle
+ * @see pv.color
+ */
+
+/**
+ * Default properties for dots. By default, there is no fill and the stroke
+ * style is a categorical color. The default shape is "circle" with size 20.
+ *
+ * @type pv.Dot
+ */
+pv.Dot.prototype.defaults = new pv.Dot()
+    .extend(pv.Mark.prototype.defaults)
+    .size(20)
+    .shape("circle")
+    .lineWidth(1.5)
+    .strokeStyle(defaultStrokeStyle);
+
+/**
+ * Constructs a new dot anchor with default properties. Dots support five
+ * different anchors:<ul>
+ *
+ * <li>top
+ * <li>left
+ * <li>center
+ * <li>bottom
+ * <li>right
+ *
+ * </ul>In addition to positioning properties (left, right, top bottom), the
+ * anchors support text rendering properties (text-align, text-baseline). Text is
+ * rendered to appear outside the dot. Note that this behavior is different from
+ * other mark anchors, which default to rendering text <i>inside</i> the mark.
+ *
+ * <p>For consistency with the other mark types, the anchor positions are
+ * defined in terms of their opposite edge. For example, the top anchor defines
+ * the bottom property, such that a bar added to the top anchor grows upward.
+ *
+ * @param {string} name the anchor name; either a string or a property function.
+ * @returns {pv.Anchor}
+ */
+pv.Dot.prototype.anchor = function(name) {
+  var dot = this;
+  return pv.Mark.prototype.anchor.call(this, name)
+    .left(function(d) {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return dot.left();
+          case "right": return dot.left() + dot.radius();
+        }
+        return null;
+      })
+    .right(function(d) {
+        switch (this.name()) {
+          case "bottom":
+          case "top":
+          case "center": return dot.right();
+          case "left": return dot.right() + dot.radius();
+        }
+        return null;
+      })
+    .top(function(d) {
+        switch (this.name()) {
+          case "left":
+          case "right":
+          case "center": return dot.top();
+          case "bottom": return dot.top() + dot.radius();
+        }
+        return null;
+      })
+    .bottom(function(d) {
+        switch (this.name()) {
+          case "left":
+          case "right":
+          case "center": return dot.bottom();
+          case "top": return dot.bottom() + dot.radius();
+        }
+        return null;
+      })
+    .textAlign(function(d) {
+        switch (this.name()) {
+          case "left": return "right";
+          case "bottom":
+          case "top":
+          case "center": return "center";
+        }
+        return "left";
+      })
+    .textBaseline(function(d) {
+        switch (this.name()) {
+          case "right":
+          case "left":
+          case "center": return "middle";
+          case "bottom": return "top";
+        }
+        return "bottom";
+      });
+};
+
+/**
+ * Returns the radius of the dot, which is defined to be the square root of the
+ * {@link #size} property.
+ *
+ * @returns {number} the radius.
+ */
+pv.Dot.prototype.radius = function() {
+  return Math.sqrt(this.size());
+};
+/**
+ * Constructs a new label mark with default properties. Labels are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents a text label, allowing textual annotation of other marks or
+ * arbitrary text within the visualization. The character data must be plain
+ * text (unicode), though the text can be styled using the {@link #font}
+ * property. If rich text is needed, external HTML elements can be overlaid on
+ * the canvas by hand.
+ *
+ * <p>Labels are positioned using the box model, similarly to {@link Dot}. Thus,
+ * a label has no width or height, but merely a text anchor location. The text
+ * is positioned relative to this anchor location based on the
+ * {@link #textAlign}, {@link #textBaseline} and {@link #textMargin} properties.
+ * Furthermore, the text may be rotated using {@link #textAngle}.
+ *
+ * <p>Labels ignore events, so as to not interfere with event handlers on
+ * underlying marks, such as bars. In the future, we may support event handlers
+ * on labels.
+ *
+ * <p>See also the <a href="../../api/Label.html">Label guide</a>.
+ *
+ * @extends pv.Mark
+ */
+pv.Label = function() {
+  pv.Mark.call(this);
+};
+
+pv.Label.prototype = pv.extend(pv.Mark)
+    .property("text")
+    .property("font")
+    .property("textAngle")
+    .property("textStyle")
+    .property("textAlign")
+    .property("textBaseline")
+    .property("textMargin")
+    .property("textShadow");
+
+pv.Label.prototype.type = "label";
+
+/**
+ * The character data to render; a string. The default value of the text
+ * property is the identity function, meaning the label's associated datum will
+ * be rendered using its <tt>toString</tt>.
+ *
+ * @type string
+ * @name pv.Label.prototype.text
+ */
+
+/**
+ * The font format, per the CSS Level 2 specification. The default font is "10px
+ * sans-serif", for consistency with the HTML 5 canvas element specification.
+ * Note that since text is not wrapped, any line-height property will be
+ * ignored. The other font-style, font-variant, font-weight, font-size and
+ * font-family properties are supported.
+ *
+ * @see <a href="http://www.w3.org/TR/CSS2/fonts.html#font-shorthand">CSS2 fonts</a>
+ * @type string
+ * @name pv.Label.prototype.font
+ */
+
+/**
+ * The rotation angle, in radians. Text is rotated clockwise relative to the
+ * anchor location. For example, with the default left alignment, an angle of
+ * Math.PI / 2 causes text to proceed downwards. The default angle is zero.
+ *
+ * @type number
+ * @name pv.Label.prototype.textAngle
+ */
+
+/**
+ * The text color. The name "textStyle" is used for consistency with "fillStyle"
+ * and "strokeStyle", although it might be better to rename this property (and
+ * perhaps use the same name as "strokeStyle"). The default color is black.
+ *
+ * @type string
+ * @name pv.Label.prototype.textStyle
+ * @see pv.color
+ */
+
+/**
+ * The horizontal text alignment. One of:<ul>
+ *
+ * <li>left
+ * <li>center
+ * <li>right
+ *
+ * </ul>The default horizontal alignment is left.
+ *
+ * @type string
+ * @name pv.Label.prototype.textAlign
+ */
+
+/**
+ * The vertical text alignment. One of:<ul>
+ *
+ * <li>top
+ * <li>middle
+ * <li>bottom
+ *
+ * </ul>The default vertical alignment is bottom.
+ *
+ * @type string
+ * @name pv.Label.prototype.textBaseline
+ */
+
+/**
+ * The text margin; may be specified in pixels, or in font-dependent units (such
+ * as ".1ex"). The margin can be used to pad text away from its anchor location,
+ * in a direction dependent on the horizontal and vertical alignment
+ * properties. For example, if the text is left- and middle-aligned, the margin
+ * shifts the text to the right. The default margin is 3 pixels.
+ *
+ * @type number
+ * @name pv.Label.prototype.textMargin
+ */
+
+/**
+ * A list of shadow effects to be applied to text, per the CSS Text Level 3
+ * text-shadow property. An example specification is "0.1em 0.1em 0.1em
+ * rgba(0,0,0,.5)"; the first length is the horizontal offset, the second the
+ * vertical offset, and the third the blur radius.
+ *
+ * @see <a href="http://www.w3.org/TR/css3-text/#text-shadow">CSS3 text</a>
+ * @type string
+ * @name pv.Label.prototype.textShadow
+ */
+
+/**
+ * Default properties for labels. See the individual properties for the default
+ * values.
+ *
+ * @type pv.Label
+ */
+pv.Label.prototype.defaults = new pv.Label()
+    .extend(pv.Mark.prototype.defaults)
+    .text(pv.identity)
+    .font("10px sans-serif")
+    .textAngle(0)
+    .textStyle("black")
+    .textAlign("left")
+    .textBaseline("bottom")
+    .textMargin(3);
+/**
+ * Constructs a new line mark with default properties. Lines are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents a series of connected line segments, or <i>polyline</i>,
+ * that can be stroked with a configurable color and thickness. Each
+ * articulation point in the line corresponds to a datum; for <i>n</i> points,
+ * <i>n</i>-1 connected line segments are drawn. The point is positioned using
+ * the box model. Arbitrary paths are also possible, allowing radar plots and
+ * other custom visualizations.
+ *
+ * <p>Like areas, lines can be stroked and filled with arbitrary colors. In most
+ * cases, lines are only stroked, but the fill style can be used to construct
+ * arbitrary polygons.
+ *
+ * <p>See also the <a href="../../api/Line.html">Line guide</a>.
+ *
+ * @extends pv.Mark
+ */
+pv.Line = function() {
+  pv.Mark.call(this);
+};
+
+pv.Line.prototype = pv.extend(pv.Mark)
+    .property("lineWidth")
+    .property("strokeStyle")
+    .property("fillStyle")
+    .property("segmented")
+    .property("interpolate");
+
+pv.Line.prototype.type = "line";
+
+/**
+ * The width of stroked lines, in pixels; used in conjunction with
+ * <tt>strokeStyle</tt> to stroke the line.
+ *
+ * @type number
+ * @name pv.Line.prototype.lineWidth
+ */
+
+/**
+ * The style of stroked lines; used in conjunction with <tt>lineWidth</tt> to
+ * stroke the line. The default value of this property is a categorical color.
+ *
+ * @type string
+ * @name pv.Line.prototype.strokeStyle
+ * @see pv.color
+ */
+
+/**
+ * The line fill style; if non-null, the interior of the line is closed and
+ * filled with the specified color. The default value of this property is a
+ * null, meaning that lines are not filled by default.
+ *
+ * @type string
+ * @name pv.Line.prototype.fillStyle
+ * @see pv.color
+ */
+
+/**
+ * Whether the line is segmented; whether variations in stroke style, line width
+ * and the other properties are treated as fixed. Rendering segmented lines is
+ * noticeably slower than non-segmented lines.
+ *
+ * <p>This property is <i>fixed</i>. See {@link pv.Mark}.
+ *
+ * @type boolean
+ * @name pv.Line.prototype.segmented
+ */
+
+/**
+ * How to interpolate between values. Linear interpolation ("linear") is the
+ * default, producing a straight line between points. For piecewise constant
+ * functions (i.e., step functions), either "step-before" or "step-after" can be
+ * specified.
+ *
+ * <p>Note: this property is currently supported only on non-segmented lines.
+ *
+ * <p>This property is <i>fixed</i>. See {@link pv.Mark}.
+ *
+ * @type string
+ * @name pv.Line.prototype.interpolate
+ */
+
+/**
+ * Default properties for lines. By default, there is no fill and the stroke
+ * style is a categorical color. The default interpolation is linear.
+ *
+ * @type pv.Line
+ */
+pv.Line.prototype.defaults = new pv.Line()
+    .extend(pv.Mark.prototype.defaults)
+    .lineWidth(1.5)
+    .strokeStyle(defaultStrokeStyle)
+    .interpolate("linear");
+
+/** @private */
+var pv_Line_specials = {left:1, top:1, right:1, bottom:1, name:1};
+
+/** @private */
+pv.Line.prototype.bind = function() {
+  pv.Mark.prototype.bind.call(this);
+  var binds = this.binds,
+      properties = binds.properties,
+      specials = binds.specials = [];
+  for (var i = 0, n = properties.length; i < n; i++) {
+    var p = properties[i];
+    if (p.name in pv_Line_specials) specials.push(p);
+  }
+};
+
+/** @private */
+pv.Line.prototype.buildInstance = function(s) {
+  if (this.index && !this.scene[0].segmented) {
+    this.buildProperties(s, this.binds.specials);
+    this.buildImplied(s);
+  } else {
+    pv.Mark.prototype.buildInstance.call(this, s);
+  }
+};
+/**
+ * Constructs a new rule with default properties. Rules are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents a horizontal or vertical rule. Rules are frequently used
+ * for axes and grid lines. For example, specifying only the bottom property
+ * draws horizontal rules, while specifying only the left draws vertical
+ * rules. Rules can also be used as thin bars. The visual style is controlled in
+ * the same manner as lines.
+ *
+ * <p>Rules are positioned exclusively the standard box model properties. The
+ * following combinations of properties are supported:
+ *
+ * <table>
+ * <thead><th style="width:12em;">Properties</th><th>Orientation</th></thead>
+ * <tbody>
+ * <tr><td>left</td><td>vertical</td></tr>
+ * <tr><td>right</td><td>vertical</td></tr>
+ * <tr><td>left, bottom, top</td><td>vertical</td></tr>
+ * <tr><td>right, bottom, top</td><td>vertical</td></tr>
+ * <tr><td>top</td><td>horizontal</td></tr>
+ * <tr><td>bottom</td><td>horizontal</td></tr>
+ * <tr><td>top, left, right</td><td>horizontal</td></tr>
+ * <tr><td>bottom, left, right</td><td>horizontal</td></tr>
+ * <tr><td>left, top, height</td><td>vertical</td></tr>
+ * <tr><td>left, bottom, height</td><td>vertical</td></tr>
+ * <tr><td>right, top, height</td><td>vertical</td></tr>
+ * <tr><td>right, bottom, height</td><td>vertical</td></tr>
+ * <tr><td>left, top, width</td><td>horizontal</td></tr>
+ * <tr><td>left, bottom, width</td><td>horizontal</td></tr>
+ * <tr><td>right, top, width</td><td>horizontal</td></tr>
+ * <tr><td>right, bottom, width</td><td>horizontal</td></tr>
+ * </tbody>
+ * </table>
+ *
+ * <p>Small rules can be used as tick marks; alternatively, a {@link Dot} with
+ * the "tick" shape can be used.
+ *
+ * <p>See also the <a href="../../api/Rule.html">Rule guide</a>.
+ *
+ * @see pv.Line
+ * @extends pv.Mark
+ */
+pv.Rule = function() {
+  pv.Mark.call(this);
+};
+
+pv.Rule.prototype = pv.extend(pv.Mark)
+    .property("width")
+    .property("height")
+    .property("lineWidth")
+    .property("strokeStyle");
+
+pv.Rule.prototype.type = "rule";
+
+/**
+ * The width of the rule, in pixels. If the left position is specified, the rule
+ * extends rightward from the left edge; if the right position is specified, the
+ * rule extends leftward from the right edge.
+ *
+ * @type number
+ * @name pv.Rule.prototype.width
+ */
+
+/**
+ * The height of the rule, in pixels. If the bottom position is specified, the
+ * rule extends upward from the bottom edge; if the top position is specified,
+ * the rule extends downward from the top edge.
+ *
+ * @type number
+ * @name pv.Rule.prototype.height
+ */
+
+/**
+ * The width of stroked lines, in pixels; used in conjunction with
+ * <tt>strokeStyle</tt> to stroke the rule. The default value is 1 pixel.
+ *
+ * @type number
+ * @name pv.Rule.prototype.lineWidth
+ */
+
+/**
+ * The style of stroked lines; used in conjunction with <tt>lineWidth</tt> to
+ * stroke the rule. The default value of this property is black.
+ *
+ * @type string
+ * @name pv.Rule.prototype.strokeStyle
+ * @see pv.color
+ */
+
+/**
+ * Default properties for rules. By default, a single-pixel black line is
+ * stroked.
+ *
+ * @type pv.Rule
+ */
+pv.Rule.prototype.defaults = new pv.Rule()
+    .extend(pv.Mark.prototype.defaults)
+    .lineWidth(1)
+    .strokeStyle("black");
+
+/**
+ * Constructs a new rule anchor with default properties. Rules support five
+ * different anchors:<ul>
+ *
+ * <li>top
+ * <li>left
+ * <li>center
+ * <li>bottom
+ * <li>right
+ *
+ * </ul>In addition to positioning properties (left, right, top bottom), the
+ * anchors support text rendering properties (text-align, text-baseline). Text is
+ * rendered to appear outside the rule. Note that this behavior is different
+ * from other mark anchors, which default to rendering text <i>inside</i> the
+ * mark.
+ *
+ * <p>For consistency with the other mark types, the anchor positions are
+ * defined in terms of their opposite edge. For example, the top anchor defines
+ * the bottom property, such that a bar added to the top anchor grows upward.
+ *
+ * @param {string} name the anchor name; either a string or a property function.
+ * @returns {pv.Anchor}
+ */
+pv.Rule.prototype.anchor = function(name) {
+  return pv.Bar.prototype.anchor.call(this, name)
+    .textAlign(function(d) {
+        switch (this.name()) {
+          case "left": return "right";
+          case "bottom":
+          case "top":
+          case "center": return "center";
+          case "right": return "left";
+        }
+      })
+    .textBaseline(function(d) {
+        switch (this.name()) {
+          case "right":
+          case "left":
+          case "center": return "middle";
+          case "top": return "bottom";
+          case "bottom": return "top";
+        }
+      });
+};
+
+/**
+ * @private Overrides the default behavior of {@link pv.Mark.buildImplied} to
+ * determine the orientation (vertical or horizontal) of the rule.
+ *
+ * @param s a node in the scene graph; the instance of the rule to build.
+ */
+pv.Rule.prototype.buildImplied = function(s) {
+  var l = s.left, r = s.right, t = s.top, b = s.bottom;
+
+  /* Determine horizontal or vertical orientation. */
+  if ((s.width != null)
+      || ((l == null) && (r == null))
+      || ((r != null) && (l != null))) {
+    s.height = 0;
+  } else {
+    s.width = 0;
+  }
+
+  pv.Mark.prototype.buildImplied.call(this, s);
+};
+/**
+ * Constructs a new, empty panel with default properties. Panels, with the
+ * exception of the root panel, are not typically constructed directly; instead,
+ * they are added to an existing panel or mark via {@link pv.Mark#add}.
+ *
+ * @class Represents a container mark. Panels allow repeated or nested
+ * structures, commonly used in small multiple displays where a small
+ * visualization is tiled to facilitate comparison across one or more
+ * dimensions. Other types of visualizations may benefit from repeated and
+ * possibly overlapping structure as well, such as stacked area charts. Panels
+ * can also offset the position of marks to provide padding from surrounding
+ * content.
+ *
+ * <p>All Protovis displays have at least one panel; this is the root panel to
+ * which marks are rendered. The box model properties (four margins, width and
+ * height) are used to offset the positions of contained marks. The data
+ * property determines the panel count: a panel is generated once per associated
+ * datum. When nested panels are used, property functions can declare additional
+ * arguments to access the data associated with enclosing panels.
+ *
+ * <p>Panels can be rendered inline, facilitating the creation of sparklines.
+ * This allows designers to reuse browser layout features, such as text flow and
+ * tables; designers can also overlay HTML elements such as rich text and
+ * images.
+ *
+ * <p>All panels have a <tt>children</tt> array (possibly empty) containing the
+ * child marks in the order they were added. Panels also have a <tt>root</tt>
+ * field which points to the root (outermost) panel; the root panel's root field
+ * points to itself.
+ *
+ * <p>See also the <a href="../../api/">Protovis guide</a>.
+ *
+ * @extends pv.Bar
+ */
+pv.Panel = function() {
+  pv.Bar.call(this);
+
+  /**
+   * The child marks; zero or more {@link pv.Mark}s in the order they were
+   * added.
+   *
+   * @see #add
+   * @type pv.Mark[]
+   */
+  this.children = [];
+  this.root = this;
+
+  /**
+   * The internal $dom field is set by the Protovis loader; see lang/init.js. It
+   * refers to the script element that contains the Protovis specification, so
+   * that the panel knows where in the DOM to insert the generated SVG element.
+   *
+   * @private
+   */
+  this.$dom = pv.Panel.$dom;
+};
+
+pv.Panel.prototype = pv.extend(pv.Bar)
+    .property("canvas")
+    .property("overflow");
+
+pv.Panel.prototype.type = "panel";
+
+/**
+ * The canvas element; either the string ID of the canvas element in the current
+ * document, or a reference to the canvas element itself. If null, a canvas
+ * element will be created and inserted into the document at the location of the
+ * script element containing the current Protovis specification. This property
+ * only applies to root panels and is ignored on nested panels.
+ *
+ * <p>Note: the "canvas" element here refers to a <tt>div</tt> (or other suitable
+ * HTML container element), <i>not</i> a <tt>canvas</tt> element. The name of
+ * this property is a historical anachronism from the first implementation that
+ * used HTML 5 canvas, rather than SVG.
+ *
+ * @type string
+ * @name pv.Panel.prototype.canvas
+ */
+
+/**
+ * Default properties for panels. By default, the margins are zero, the fill
+ * style is transparent.
+ *
+ * @type pv.Panel
+ */
+pv.Panel.prototype.defaults = new pv.Panel()
+    .extend(pv.Bar.prototype.defaults)
+    .fillStyle(null)
+    .overflow("visible");
+
+/**
+ * Returns an anchor with the specified name. This method is overridden since
+ * the behavior of Panel anchors is slightly different from normal anchors:
+ * adding to an anchor adds to the anchor target's, rather than the anchor
+ * target's parent. To avoid double margins, we override the anchor's proto so
+ * that the margins are zero.
+ *
+ * @param {string} name the anchor name; either a string or a property function.
+ * @returns {pv.Anchor} the new anchor.
+ */
+pv.Panel.prototype.anchor = function(name) {
+
+  /* A "view" of this panel whose margins appear to be zero. */
+  function z() { return 0; }
+  z.prototype = this;
+  z.prototype.left = z.prototype.right = z.prototype.top = z.prototype.bottom = z;
+
+  var anchor = pv.Bar.prototype.anchor.call(new z(), name)
+      .data(function(d) { return [d]; });
+  anchor.parent = this;
+  return anchor;
+};
+
+/**
+ * Adds a new mark of the specified type to this panel. Unlike the normal
+ * {@link Mark#add} behavior, adding a mark to a panel does not cause the mark
+ * to inherit from the panel. Since the contained marks are offset by the panel
+ * margins already, inheriting properties is generally undesirable; of course,
+ * it is always possible to change this behavior by calling {@link Mark#extend}
+ * explicitly.
+ *
+ * @param {function} type the type of the new mark to add.
+ * @returns {pv.Mark} the new mark.
+ */
+pv.Panel.prototype.add = function(type) {
+  var child = new type();
+  child.parent = this;
+  child.root = this.root;
+  child.childIndex = this.children.length;
+  this.children.push(child);
+  return child;
+};
+
+/** @private TODO */
+pv.Panel.prototype.bind = function() {
+  pv.Mark.prototype.bind.call(this);
+  for (var i = 0; i < this.children.length; i++) {
+    this.children[i].bind();
+  }
+};
+
+/**
+ * @private Evaluates all of the properties for this panel for the specified
+ * instance <tt>s</tt> in the scene graph, including recursively building the
+ * scene graph for child marks.
+ *
+ * @param s a node in the scene graph; the instance of the panel to build.
+ * @see Mark#scene
+ */
+pv.Panel.prototype.buildInstance = function(s) {
+  pv.Bar.prototype.buildInstance.call(this, s);
+  if (!s.children) s.children = [];
+
+  /*
+   * Build each child, passing in the parent (this panel) scene graph node. The
+   * child mark's scene is initialized from the corresponding entry in the
+   * existing scene graph, such that properties from the previous build can be
+   * reused; this is largely to facilitate the recycling of SVG elements.
+   */
+  for (var i = 0; i < this.children.length; i++) {
+    this.children[i].scene = s.children[i]; // possibly undefined
+    this.children[i].build();
+  }
+
+  /*
+   * Once the child marks have been built, the new scene graph nodes are removed
+   * from the child marks and placed into the scene graph. The nodes cannot
+   * remain on the child nodes because this panel (or a parent panel) may be
+   * instantiated multiple times!
+   */
+  for (var i = 0; i < this.children.length; i++) {
+    s.children[i] = this.children[i].scene;
+    delete this.children[i].scene;
+  }
+
+  /* Delete any expired child scenes, should child marks have been removed. */
+  s.children.length = this.children.length;
+};
+
+/**
+ * @private Computes the implied properties for this panel for the specified
+ * instance <tt>s</tt> in the scene graph. Panels have two implied
+ * properties:<ul>
+ *
+ * <li>The <tt>canvas</tt> property references the DOM element, typically a DIV,
+ * that contains the SVG element that is used to display the visualization. This
+ * property may be specified as a string, referring to the unique ID of the
+ * element in the DOM. The string is converted to a reference to the DOM
+ * element. The width and height of the SVG element is inferred from this DOM
+ * element. If no canvas property is specified, a new SVG element is created and
+ * inserted into the document, using the panel dimensions; see
+ * {@link #createCanvas}.
+ *
+ * <li>The <tt>children</tt> array, while not a property per se, contains the
+ * scene graph for each child mark. This array is initialized to be empty, and
+ * is populated above in {@link #buildInstance}.
+ *
+ * </ul>The current implementation creates the SVG element, if necessary, during
+ * the build phase; in the future, it may be preferrable to move this to the
+ * update phase, although then the canvas property would be undefined. In
+ * addition, DOM inspection is necessary to define the implied width and height
+ * properties that may be inferred from the DOM.
+ *
+ * @param s a node in the scene graph; the instance of the panel to build.
+ */
+pv.Panel.prototype.buildImplied = function(s) {
+  if (!this.parent) {
+    var c = s.canvas;
+    if (c) {
+      if (typeof c == "string") c = document.getElementById(c);
+
+      /* Clear the container if it's not associated with this panel. */
+      if (c.$panel != this) {
+        c.$panel = this;
+        c.innerHTML = "";
+      }
+
+      /* If width and height weren't specified, inspect the container. */
+      var w, h;
+      if (s.width == null) {
+        w = parseFloat(pv.css(c, "width"));
+        s.width = w - s.left - s.right;
+      }
+      if (s.height == null) {
+        h = parseFloat(pv.css(c, "height"));
+        s.height = h - s.top - s.bottom;
+      }
+    } else if (s.$canvas) {
+
+      /*
+       * If the canvas property is null, and we previously created a canvas for
+       * this scene node, reuse the previous canvas rather than creating a new
+       * one.
+       */
+      c = s.$canvas;
+    } else {
+
+      /**
+       * Returns the last element in the current document's body. The canvas
+       * element is appended to this last element if another DOM element has not
+       * already been specified via the <tt>$dom</tt> field.
+       */
+      function lastElement() {
+        var node = document.body;
+        while (node.lastChild && node.lastChild.tagName) {
+          node = node.lastChild;
+        }
+        return (node == document.body) ? node : node.parentNode;
+      }
+
+      /* Insert a new container into the DOM. */
+      c = s.$canvas = document.createElement("span");
+      this.$dom // script element for text/javascript+protovis
+          ? this.$dom.parentNode.insertBefore(c, this.$dom)
+          : lastElement().appendChild(c);
+    }
+    s.canvas = c;
+  }
+  pv.Bar.prototype.buildImplied.call(this, s);
+};
+/**
+ * Constructs a new dot mark with default properties. Images are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents an image. Images share the same layout and style properties as
+ * bars, in conjunction with an external image such as PNG or JPEG. The image is
+ * specified via the {@link #url} property. The fill, if specified, appears
+ * beneath the image, while the optional stroke appears above the image.
+ *
+ * <p>TODO Restore support for dynamic images (such as heatmaps). These were
+ * supported in the canvas implementation using the pixel buffer API; although
+ * SVG does not support pixel manipulation, it is possible to embed a canvas
+ * element in SVG using foreign objects.
+ *
+ * <p>TODO Allow different modes of image placement: "scale" -- scale and
+ * preserve aspect ratio, "tile" -- repeat the image, "center" -- center the
+ * image, "fill" -- scale without preserving aspect ratio.
+ *
+ * <p>See {@link pv.Bar} for details on positioning properties.
+ *
+ * @extends pv.Bar
+ */
+pv.Image = function() {
+  pv.Bar.call(this);
+};
+
+pv.Image.prototype = pv.extend(pv.Bar)
+    .property("url");
+
+pv.Image.prototype.type = "image";
+
+/**
+ * The URL of the image to display. The set of supported image types is
+ * browser-dependent; PNG and JPEG are recommended.
+ *
+ * @type string
+ * @name pv.Image.prototype.url
+ */
+
+/**
+ * Default properties for images. By default, there is no stroke or fill style.
+ *
+ * @type pv.Image
+ */
+pv.Image.prototype.defaults = new pv.Image()
+    .extend(pv.Bar.prototype.defaults)
+    .fillStyle(null);
+/**
+ * Constructs a new wedge with default properties. Wedges are not typically
+ * constructed directly, but by adding to a panel or an existing mark via
+ * {@link pv.Mark#add}.
+ *
+ * @class Represents a wedge, or pie slice. Specified in terms of start and end
+ * angle, inner and outer radius, wedges can be used to construct donut charts
+ * and polar bar charts as well. If the {@link #angle} property is used, the end
+ * angle is implied by adding this value to start angle. By default, the start
+ * angle is the previously-generated wedge's end angle. This design allows
+ * explicit control over the wedge placement if desired, while offering
+ * convenient defaults for the construction of radial graphs.
+ *
+ * <p>The center point of the circle is positioned using the standard box model.
+ * The wedge can be stroked and filled, similar to {link Bar}.
+ *
+ * <p>See also the <a href="../../api/Wedge.html">Wedge guide</a>.
+ *
+ * @extends pv.Mark
+ */
+pv.Wedge = function() {
+  pv.Mark.call(this);
+};
+
+pv.Wedge.prototype = pv.extend(pv.Mark)
+    .property("startAngle")
+    .property("endAngle")
+    .property("angle")
+    .property("innerRadius")
+    .property("outerRadius")
+    .property("lineWidth")
+    .property("strokeStyle")
+    .property("fillStyle");
+
+pv.Wedge.prototype.type = "wedge";
+
+/**
+ * The start angle of the wedge, in radians. The start angle is measured
+ * clockwise from the 3 o'clock position. The default value of this property is
+ * the end angle of the previous instance (the {@link Mark#sibling}), or -PI / 2
+ * for the first wedge; for pie and donut charts, typically only the
+ * {@link #angle} property needs to be specified.
+ *
+ * @type number
+ * @name pv.Wedge.prototype.startAngle
+ */
+
+/**
+ * The end angle of the wedge, in radians. If not specified, the end angle is
+ * implied as the start angle plus the {@link #angle}.
+ *
+ * @type number
+ * @name pv.Wedge.prototype.endAngle
+ */
+
+/**
+ * The angular span of the wedge, in radians. This property is used if end angle
+ * is not specified.
+ *
+ * @type number
+ * @name pv.Wedge.prototype.angle
+ */
+
+/**
+ * The inner radius of the wedge, in pixels. The default value of this property
+ * is zero; a positive value will produce a donut slice rather than a pie slice.
+ * The inner radius can vary per-wedge.
+ *
+ * @type number
+ * @name pv.Wedge.prototype.innerRadius
+ */
+
+/**
+ * The outer radius of the wedge, in pixels. This property is required. For
+ * pies, only this radius is required; for donuts, the inner radius must be
+ * specified as well. The outer radius can vary per-wedge.
+ *
+ * @type number
+ * @name pv.Wedge.prototype.outerRadius
+ */
+
+/**
+ * The width of stroked lines, in pixels; used in conjunction with
+ * <tt>strokeStyle</tt> to stroke the wedge's border.
+ *
+ * @type number
+ * @name pv.Wedge.prototype.lineWidth
+ */
+
+/**
+ * The style of stroked lines; used in conjunction with <tt>lineWidth</tt> to
+ * stroke the wedge's border. The default value of this property is null,
+ * meaning wedges are not stroked by default.
+ *
+ * @type string
+ * @name pv.Wedge.prototype.strokeStyle
+ * @see pv.color
+ */
+
+/**
+ * The wedge fill style; if non-null, the interior of the wedge is filled with
+ * the specified color. The default value of this property is a categorical
+ * color.
+ *
+ * @type string
+ * @name pv.Wedge.prototype.fillStyle
+ * @see pv.color
+ */
+
+/**
+ * Default properties for wedges. By default, there is no stroke and the fill
+ * style is a categorical color.
+ *
+ * @type pv.Wedge
+ */
+pv.Wedge.prototype.defaults = new pv.Wedge()
+    .extend(pv.Mark.prototype.defaults)
+    .startAngle(function() {
+        var s = this.sibling();
+        return s ? s.endAngle : -Math.PI / 2;
+      })
+    .innerRadius(0)
+    .lineWidth(1.5)
+    .strokeStyle(null)
+    .fillStyle(defaultFillStyle.by(pv.index));
+
+/**
+ * Returns the mid-radius of the wedge, which is defined as half-way between the
+ * inner and outer radii.
+ *
+ * @see #innerRadius
+ * @see #outerRadius
+ * @returns {number} the mid-radius, in pixels.
+ */
+pv.Wedge.prototype.midRadius = function() {
+  return (this.innerRadius() + this.outerRadius()) / 2;
+};
+
+/**
+ * Returns the mid-angle of the wedge, which is defined as half-way between the
+ * start and end angles.
+ *
+ * @see #startAngle
+ * @see #endAngle
+ * @returns {number} the mid-angle, in radians.
+ */
+pv.Wedge.prototype.midAngle = function() {
+  return (this.startAngle() + this.endAngle()) / 2;
+};
+
+/**
+ * Constructs a new wedge anchor with default properties. Wedges support five
+ * different anchors:<ul>
+ *
+ * <li>outer
+ * <li>inner
+ * <li>center
+ * <li>start
+ * <li>end
+ *
+ * </ul>In addition to positioning properties (left, right, top bottom), the
+ * anchors support text rendering properties (text-align, text-baseline,
+ * textAngle). Text is rendered to appear inside the wedge.
+ *
+ * @param {string} name the anchor name; either a string or a property function.
+ * @returns {pv.Anchor}
+ */
+pv.Wedge.prototype.anchor = function(name) {
+  var w = this;
+  return pv.Mark.prototype.anchor.call(this, name)
+    .left(function() {
+        switch (this.name()) {
+          case "outer": return w.left() + w.outerRadius() * Math.cos(w.midAngle());
+          case "inner": return w.left() + w.innerRadius() * Math.cos(w.midAngle());
+          case "start": return w.left() + w.midRadius() * Math.cos(w.startAngle());
+          case "center": return w.left() + w.midRadius() * Math.cos(w.midAngle());
+          case "end": return w.left() + w.midRadius() * Math.cos(w.endAngle());
+        }
+      })
+    .right(function() {
+        switch (this.name()) {
+          case "outer": return w.right() + w.outerRadius() * Math.cos(w.midAngle());
+          case "inner": return w.right() + w.innerRadius() * Math.cos(w.midAngle());
+          case "start": return w.right() + w.midRadius() * Math.cos(w.startAngle());
+          case "center": return w.right() + w.midRadius() * Math.cos(w.midAngle());
+          case "end": return w.right() + w.midRadius() * Math.cos(w.endAngle());
+        }
+      })
+    .top(function() {
+        switch (this.name()) {
+          case "outer": return w.top() + w.outerRadius() * Math.sin(w.midAngle());
+          case "inner": return w.top() + w.innerRadius() * Math.sin(w.midAngle());
+          case "start": return w.top() + w.midRadius() * Math.sin(w.startAngle());
+          case "center": return w.top() + w.midRadius() * Math.sin(w.midAngle());
+          case "end": return w.top() + w.midRadius() * Math.sin(w.endAngle());
+        }
+      })
+    .bottom(function() {
+        switch (this.name()) {
+          case "outer": return w.bottom() + w.outerRadius() * Math.sin(w.midAngle());
+          case "inner": return w.bottom() + w.innerRadius() * Math.sin(w.midAngle());
+          case "start": return w.bottom() + w.midRadius() * Math.sin(w.startAngle());
+          case "center": return w.bottom() + w.midRadius() * Math.sin(w.midAngle());
+          case "end": return w.bottom() + w.midRadius() * Math.sin(w.endAngle());
+        }
+      })
+    .textAlign(function() {
+        switch (this.name()) {
+          case "outer": return pv.Wedge.upright(w.midAngle()) ? "right" : "left";
+          case "inner": return pv.Wedge.upright(w.midAngle()) ? "left" : "right";
+        }
+        return "center";
+      })
+    .textBaseline(function() {
+        switch (this.name()) {
+          case "start": return pv.Wedge.upright(w.startAngle()) ? "top" : "bottom";
+          case "end": return pv.Wedge.upright(w.endAngle()) ? "bottom" : "top";
+        }
+        return "middle";
+      })
+    .textAngle(function() {
+        var a = 0;
+        switch (this.name()) {
+          case "center":
+          case "inner":
+          case "outer": a = w.midAngle(); break;
+          case "start": a = w.startAngle(); break;
+          case "end": a = w.endAngle(); break;
+        }
+        return pv.Wedge.upright(a) ? a : (a + Math.PI);
+      });
+};
+
+/**
+ * Returns true if the specified angle is considered "upright", as in, text
+ * rendered at that angle would appear upright. If the angle is not upright,
+ * text is rotated 180 degrees to be upright, and the text alignment properties
+ * are correspondingly changed.
+ *
+ * @param {number} angle an angle, in radius.
+ * @returns {boolean} true if the specified angle is upright.
+ */
+pv.Wedge.upright = function(angle) {
+  angle = angle % (2 * Math.PI);
+  angle = (angle < 0) ? (2 * Math.PI + angle) : angle;
+  return (angle < Math.PI / 2) || (angle > 3 * Math.PI / 2);
+};
+
+/**
+ * @private Overrides the default behavior of {@link pv.Mark.buildImplied} such
+ * that the end angle is computed from the start angle and angle (angular span)
+ * if not specified.
+ *
+ * @param s a node in the scene graph; the instance of the wedge to build.
+ */
+pv.Wedge.prototype.buildImplied = function(s) {
+  pv.Mark.prototype.buildImplied.call(this, s);
+
+  /*
+   * TODO If the angle or endAngle is updated by an event handler, the implied
+   * properties won't recompute correctly, so this will lead to potentially
+   * buggy redraw. How to re-evaluate implied properties on update?
+   */
+  if (s.endAngle == null) s.endAngle = s.startAngle + s.angle;
+  if (s.angle == null) s.angle = s.endAngle - s.startAngle;
+};
+/**
+ * @ignore
+ * @namespace
+ */
+pv.Layout = {};
+/**
+ * Returns a new grid layout.
+ *
+ * @class A grid layout with regularly-sized rows and columns. <img
+ * src="../grid.png" width="160" height="160" align="right"> The number of rows
+ * and columns are determined from the array, which should be in row-major
+ * order. For example, the 2&times;3 array:
+ *
+ * <pre>1 2 3
+ * 4 5 6</pre>
+ *
+ * should be represented as:
+ *
+ * <pre>[[1, 2, 3], [4, 5, 6]]</pre>
+ *
+ * If your data is in column-major order, you can use {@link pv.transpose} to
+ * transpose it.
+ *
+ * <p>This layout defines left, top, width, height and data properties. The data
+ * property will be the associated element in the array. For example, if the
+ * array is a two-dimensional array of values in the range [0,1], a simple
+ * heatmap can be generated as:
+ *
+ * <pre>.add(pv.Bar)
+ *   .extend(pv.Layout.grid(array))
+ *   .fillStyle(pv.ramp("white", "black"))</pre>
+ *
+ * By default, the grid fills the full width and height of the parent panel.
+ *
+ * @param {array[]} arrays an array of arrays.
+ * @returns {pv.Layout.grid} a grid layout.
+ */
+pv.Layout.grid = function(arrays) {
+  var rows = arrays.length, cols = arrays[0].length;
+
+  /** @private */
+  function w() { return this.parent.width() / cols; }
+
+  /** @private */
+  function h() { return this.parent.height() / rows; }
+
+  /* A dummy mark, like an anchor, which the caller extends. */
+  return new pv.Mark()
+      .data(pv.blend(arrays))
+      .left(function() { return w.call(this) * (this.index % cols); })
+      .top(function() { return h.call(this) * Math.floor(this.index / cols); })
+      .width(w)
+      .height(h);
+};
+/**
+ * Returns a new stack layout.
+ *
+ * @class A layout for stacking marks vertically or horizontally, using the
+ * <i>cousin</i> instance. This layout is designed to be used for one of the
+ * four positional properties in the box model, and changes behavior depending
+ * on the property being evaluated:<ul>
+ *
+ * <li>bottom: cousin.bottom + cousin.height
+ * <li>top: cousin.top + cousin.height
+ * <li>left: cousin.left + cousin.width
+ * <li>right: cousin.right + cousin.width
+ *
+ * </ul>If no cousin instance is available (for example, for first instance),
+ * the specified offset is used. If no offset is specified, zero is used. For
+ * example,
+ *
+ * <pre>new pv.Panel()
+ *     .width(150).height(150)
+ *   .add(pv.Panel)
+ *     .data([[1, 1.2, 1.7, 1.5, 1.7],
+ *            [.5, 1, .8, 1.1, 1.3],
+ *            [.2, .5, .8, .9, 1]])
+ *   .add(pv.Area)
+ *     .data(function(d) d)
+ *     .bottom(pv.Layout.stack())
+ *     .height(function(d) d * 40)
+ *     .left(function() this.index * 35)
+ *   .root.render();</pre>
+ *
+ * specifies a vertically-stacked area chart.
+ *
+ * @returns {pv.Layout.stack} a stack property function.
+ * @see pv.Mark#cousin
+ */
+pv.Layout.stack = function() {
+  /** @private */
+  var offset = function() { return 0; };
+
+  /** @private */
+  function layout() {
+
+    /* Find the previous visible parent instance. */
+    var i = this.parent.index, p, c;
+    while ((i-- > 0) && !c) {
+      p = this.parent.scene[i];
+      if (p.visible) c = p.children[this.childIndex][this.index];
+    }
+
+    if (c) {
+      switch (property) {
+        case "bottom": return c.bottom + c.height;
+        case "top": return c.top + c.height;
+        case "left": return c.left + c.width;
+        case "right": return c.right + c.width;
+      }
+    }
+
+    return offset.apply(this, arguments);
+  }
+
+  /**
+   * Sets the offset for this stack layout. The offset can either be specified
+   * as a function or as a constant. If a function, the function is invoked in
+   * the same context as a normal property function: <tt>this</tt> refers to the
+   * mark, and the arguments are the full data stack. By default the offset is
+   * zero.
+   *
+   * @function
+   * @name pv.Layout.stack.prototype.offset
+   * @param {function} f offset function, or constant value.
+   * @returns {pv.Layout.stack} this.
+   */
+  layout.offset = function(f) {
+      offset = (f instanceof Function) ? f : function() { return f; };
+      return this;
+    };
+
+  return layout;
+};
+// TODO share code with Treemap
+// TODO vertical / horizontal orientation?
+
+/**
+ * Returns a new icicle tree layout.
+ *
+ * @class A tree layout in the form of an icicle. <img src="../icicle.png"
+ * width="160" height="160" align="right"> The first row corresponds to the root
+ * of the tree; subsequent rows correspond to each tier. Rows are subdivided
+ * into cells based on the size of nodes, per {@link #size}. Within a row, cells
+ * are sorted by size.
+ *
+ * <p>This tree layout is intended to be extended (see {@link pv.Mark#extend})
+ * by a {@link pv.Bar}. The data property returns an array of nodes for use by
+ * other property functions. The following node attributes are supported:
+ *
+ * <ul>
+ * <li><tt>left</tt> - the cell left position.
+ * <li><tt>top</tt> - the cell top position.
+ * <li><tt>width</tt> - the cell width.
+ * <li><tt>height</tt> - the cell height.
+ * <li><tt>depth</tt> - the node depth (tier; the root is 0).
+ * <li><tt>keys</tt> - an array of string keys for the node.
+ * <li><tt>size</tt> - the aggregate node size.
+ * <li><tt>children</tt> - child nodes, if any.
+ * <li><tt>data</tt> - the associated tree element, for leaf nodes.
+ * </ul>
+ *
+ * To produce a default icicle layout, say:
+ *
+ * <pre>.add(pv.Bar)
+ *   .extend(pv.Layout.icicle(tree))</pre>
+ *
+ * To customize the tree to highlight leaf nodes bigger than 10,000 (1E4), you
+ * might say:
+ *
+ * <pre>.add(pv.Bar)
+ *   .extend(pv.Layout.icicle(tree))
+ *   .fillStyle(function(n) n.data > 1e4 ? "#ff0" : "#fff")</pre>
+ *
+ * The format of the <tt>tree</tt> argument is any hierarchical object whose
+ * leaf nodes are numbers corresponding to their size. For an example, and
+ * information on how to convert tabular data into such a tree, see
+ * {@link pv.Tree}. If the leaf nodes are not numbers, a {@link #size} function
+ * can be specified to override how the tree is interpreted. This size function
+ * can also be used to transform the data.
+ *
+ * <p>By default, the icicle fills the full width and height of the parent
+ * panel. An optional root key can be specified using {@link #root} for
+ * convenience.
+ *
+ * @param tree a tree (an object) who leaf attributes have sizes.
+ * @returns {pv.Layout.icicle} a tree layout.
+ */
+pv.Layout.icicle = function(tree) {
+  var keys = [], sizeof = Number;
+
+  /** @private */
+  function accumulate(map) {
+    var node = {size: 0, children: [], keys: keys.slice()};
+    for (var key in map) {
+      var child = map[key], size = sizeof(child);
+      keys.push(key);
+      if (isNaN(size)) {
+        child = accumulate(child);
+      } else {
+        child = {size: size, data: child, keys: keys.slice()};
+      }
+      node.children.push(child);
+      node.size += child.size;
+      keys.pop();
+    }
+    node.children.sort(function(a, b) { return b.size - a.size; });
+    return node;
+  }
+
+  /** @private */
+  function scale(node, k) {
+    node.size *= k;
+    if (node.children) {
+      for (var i = 0; i < node.children.length; i++) {
+        scale(node.children[i], k);
+      }
+    }
+  }
+
+  /** @private */
+  function depth(node, i) {
+    i = i ? (i + 1) : 1;
+    return node.children
+        ? pv.max(node.children, function(n) { return depth(n, i); })
+        : i;
+  }
+
+  /** @private */
+  function layout(node) {
+    if (node.children) {
+      icify(node);
+      for (var i = 0; i < node.children.length; i++) {
+        layout(node.children[i]);
+      }
+    }
+  }
+
+  /** @private */
+  function icify(node) {
+    var left = node.left;
+    for (var i = 0; i < node.children.length; i++) {
+      var child = node.children[i], width = (child.size / node.size) * node.width;
+      child.left = left;
+      child.top = node.top + node.height;
+      child.width = width;
+      child.height = node.height;
+      child.depth = node.depth + 1;
+      left += width;
+      if (child.children) {
+        icify(child);
+      }
+    }
+  }
+
+  /** @private */
+  function flatten(node, array) {
+    if (node.children) {
+      for (var i = 0; i < node.children.length; i++) {
+        flatten(node.children[i], array);
+      }
+    }
+    array.push(node)
+    return array;
+  }
+
+  /** @private */
+  function data() {
+    var root = accumulate(tree);
+    root.top = 0;
+    root.left = 0;
+    root.width = this.parent.width();
+    root.height = this.parent.height() / depth(root);
+    root.depth = 0;
+    layout(root);
+    return flatten(root, []).reverse();
+  }
+
+  /* A dummy mark, like an anchor, which the caller extends. */
+  var mark = new pv.Mark()
+      .data(data)
+      .left(function(n) { return n.left; })
+      .top(function(n) { return n.top; })
+      .width(function(n) { return n.width; })
+      .height(function(n) { return n.height; });
+
+  /**
+   * Specifies the root key; optional. The root key is prepended to the
+   * <tt>keys</tt> attribute for all generated nodes. This method is provided
+   * for convenience and does not affect layout.
+   *
+   * @param {string} v the root key.
+   * @function
+   * @name pv.Layout.icicle.prototype.root
+   * @returns {pv.Layout.icicle} this.
+   */
+  mark.root = function(v) {
+    keys = [v];
+    return this;
+  };
+
+  /**
+   * Specifies the sizing function. By default, the sizing function is
+   * <tt>Number</tt>. The sizing function is invoked for each node in the tree
+   * (passed to the constructor): the sizing function must return
+   * <tt>undefined</tt> or <tt>NaN</tt> for internal nodes, and a number for
+   * leaf nodes. The aggregate sizes of internal nodes will be automatically
+   * computed by the layout.
+   *
+   * <p>For example, if the tree data structure represents a file system, with
+   * files as leaf nodes, and each file has a <tt>bytes</tt> attribute, you can
+   * specify a size function as:
+   *
+   * <pre>.size(function(d) d.bytes)</pre>
+   *
+   * This function will return <tt>undefined</tt> for internal nodes (since
+   * these do not have a <tt>bytes</tt> attribute), and a number for leaf nodes.
+   *
+   * <p>Note that the built-in <tt>Math.sqrt</tt> and <tt>Math.log</tt> methods
+   * can also be used as sizing functions. These function similarly to
+   * <tt>Number</tt>, except perform a root and log scale, respectively.
+   *
+   * @param {function} f the new sizing function.
+   * @function
+   * @name pv.Layout.icicle.prototype.size
+   * @returns {pv.Layout.icicle} this.
+   */
+  mark.size = function(f) {
+    sizeof = f;
+    return this;
+  };
+
+  return mark;
+};
+// TODO share code with Treemap
+// TODO inspect parent panel dimensions to set inner and outer radii
+
+/**
+ * Returns a new sunburst tree layout.
+ *
+ * @class A tree layout in the form of a sunburst. <img
+ * src="../sunburst.png" width="160" height="160" align="right"> The
+ * center circle corresponds to the root of the tree; subsequent rings
+ * correspond to each tier. Rings are subdivided into wedges based on the size
+ * of nodes, per {@link #size}. Within a ring, wedges are sorted by size.
+ *
+ * <p>The tree layout is intended to be extended (see {@link pv.Mark#extend} by
+ * a {@link pv.Wedge}. The data property returns an array of nodes for use by
+ * other property functions. The following node attributes are supported:
+ *
+ * <ul>
+ * <li><tt>left</tt> - the wedge left position.
+ * <li><tt>top</tt> - the wedge top position.
+ * <li><tt>innerRadius</tt> - the wedge inner radius.
+ * <li><tt>outerRadius</tt> - the wedge outer radius.
+ * <li><tt>startAngle</tt> - the wedge start angle.
+ * <li><tt>endAngle</tt> - the wedge end angle.
+ * <li><tt>angle</tt> - the wedge angle.
+ * <li><tt>depth</tt> - the node depth (tier; the root is 0).
+ * <li><tt>keys</tt> - an array of string keys for the node.
+ * <li><tt>size</tt> - the aggregate node size.
+ * <li><tt>children</tt> - child nodes, if any.
+ * <li><tt>data</tt> - the associated tree element, for leaf nodes.
+ * </ul>
+ *
+ * <p>To produce a default sunburst layout, say:
+ *
+ * <pre>.add(pv.Wedge)
+ *   .extend(pv.Layout.sunburst(tree))</pre>
+ *
+ * To only show nodes at a depth of two or greater, you might say:
+ *
+ * <pre>.add(pv.Wedge)
+ *   .extend(pv.Layout.sunburst(tree))
+ *   .visible(function(n) n.depth > 1)</pre>
+ *
+ * The format of the <tt>tree</tt> argument is a hierarchical object whose leaf
+ * nodes are numbers corresponding to their size. For an example, and
+ * information on how to convert tabular data into such a tree, see
+ * {@link pv.Tree}. If the leaf nodes are not numbers, a {@link #size} function
+ * can be specified to override how the tree is interpreted. This size function
+ * can also be used to transform the data.
+ *
+ * <p>By default, the sunburst fills the full width and height of the parent
+ * panel. An optional root key can be specified using {@link #root} for
+ * convenience.
+ *
+ * @param tree a tree (an object) who leaf attributes have sizes.
+ * @returns {pv.Layout.sunburst} a tree layout.
+ */
+pv.Layout.sunburst = function(tree) {
+  var keys = [], sizeof = Number, w, h, r;
+
+  /** @private */
+  function accumulate(map) {
+    var node = {size: 0, children: [], keys: keys.slice()};
+    for (var key in map) {
+      var child = map[key], size = sizeof(child);
+      keys.push(key);
+      if (isNaN(size)) {
+        child = accumulate(child);
+      } else {
+        child = {size: size, data: child, keys: keys.slice()};
+      }
+      node.children.push(child);
+      node.size += child.size;
+      keys.pop();
+    }
+    node.children.sort(function(a, b) { return b.size - a.size; });
+    return node;
+  }
+
+  /** @private */
+  function scale(node, k) {
+    node.size *= k;
+    if (node.children) {
+      for (var i = 0; i < node.children.length; i++) {
+        scale(node.children[i], k);
+      }
+    }
+  }
+
+  /** @private */
+  function depth(node, i) {
+    i = i ? (i + 1) : 1;
+    return node.children
+        ? pv.max(node.children, function(n) { return depth(n, i); })
+        : i;
+  }
+
+  /** @private */
+  function layout(node) {
+    if (node.children) {
+      wedgify(node);
+      for (var i = 0; i < node.children.length; i++) {
+        layout(node.children[i]);
+      }
+    }
+  }
+
+  /** @private */
+  function wedgify(node) {
+    var startAngle = node.startAngle;
+    for (var i = 0; i < node.children.length; i++) {
+      var child = node.children[i], angle = (child.size / node.size) * node.angle;
+      child.startAngle = startAngle;
+      child.angle = angle;
+      child.endAngle = startAngle + angle;
+      child.depth = node.depth + 1;
+      child.left = w / 2;
+      child.top = h / 2;
+      child.innerRadius = Math.max(0, child.depth - .5) * r;
+      child.outerRadius = (child.depth + .5) * r;
+      startAngle += angle;
+      if (child.children) {
+        wedgify(child);
+      }
+    }
+  }
+
+  /** @private */
+  function flatten(node, array) {
+    if (node.children) {
+      for (var i = 0; i < node.children.length; i++) {
+        flatten(node.children[i], array);
+      }
+    }
+    array.push(node)
+    return array;
+  }
+
+  /** @private */
+  function data() {
+    var root = accumulate(tree);
+    w = this.parent.width();
+    h = this.parent.height();
+    r = Math.min(w, h) / 2 / (depth(root) - .5);
+    root.left = w / 2;
+    root.top = h / 2;
+    root.startAngle = 0;
+    root.angle = 2 * Math.PI;
+    root.endAngle = 2 * Math.PI;
+    root.innerRadius = 0;
+    root.outerRadius = r;
+    root.depth = 0;
+    layout(root);
+    return flatten(root, []).reverse();
+  }
+
+  /* A dummy mark, like an anchor, which the caller extends. */
+  var mark = new pv.Mark()
+      .data(data)
+      .left(function(n) { return n.left; })
+      .top(function(n) { return n.top; })
+      .startAngle(function(n) { return n.startAngle; })
+      .angle(function(n) { return n.angle; })
+      .innerRadius(function(n) { return n.innerRadius; })
+      .outerRadius(function(n) { return n.outerRadius; });
+
+  /**
+   * Specifies the root key; optional. The root key is prepended to the
+   * <tt>keys</tt> attribute for all generated nodes. This method is provided
+   * for convenience and does not affect layout.
+   *
+   * @param {string} v the root key.
+   * @function
+   * @name pv.Layout.sunburst.prototype.root
+   * @returns {pv.Layout.sunburst} this.
+   */
+  mark.root = function(v) {
+    keys = [v];
+    return this;
+  };
+
+  /**
+   * Specifies the sizing function. By default, the sizing function is
+   * <tt>Number</tt>. The sizing function is invoked for each node in the tree
+   * (passed to the constructor): the sizing function must return
+   * <tt>undefined</tt> or <tt>NaN</tt> for internal nodes, and a number for
+   * leaf nodes. The aggregate sizes of internal nodes will be automatically
+   * computed by the layout.
+   *
+   * <p>For example, if the tree data structure represents a file system, with
+   * files as leaf nodes, and each file has a <tt>bytes</tt> attribute, you can
+   * specify a size function as:
+   *
+   * <pre>.size(function(d) d.bytes)</pre>
+   *
+   * This function will return <tt>undefined</tt> for internal nodes (since
+   * these do not have a <tt>bytes</tt> attribute), and a number for leaf nodes.
+   *
+   * <p>Note that the built-in <tt>Math.sqrt</tt> and <tt>Math.log</tt> methods
+   * can be used as sizing functions. These function similarly to
+   * <tt>Number</tt>, except perform a root and log scale, respectively.
+   *
+   * @param {function} f the new sizing function.
+   * @function
+   * @name pv.Layout.sunburst.prototype.size
+   * @returns {pv.Layout.sunburst} this.
+   */
+  mark.size = function(f) {
+    sizeof = f;
+    return this;
+  };
+
+  return mark;
+};
+// TODO add `by` function for determining size (and children?)
+
+/**
+ * Returns a new treemap tree layout.
+ *
+ * @class A tree layout in the form of an treemap. <img
+ * src="../treemap.png" width="160" height="160" align="right"> Treemaps
+ * are a form of space-filling layout that represents nodes as boxes, with child
+ * nodes placed within parent boxes. The size of each box is proportional to the
+ * size of the node in the tree.
+ *
+ * <p>This particular algorithm is taken from Bruls, D.M., C. Huizing, and
+ * J.J. van Wijk, <a href="http://www.win.tue.nl/~vanwijk/stm.pdf">"Squarified
+ * Treemaps"</a> in <i>Data Visualization 2000, Proceedings of the Joint
+ * Eurographics and IEEE TCVG Sumposium on Visualization</i>, 2000,
+ * pp. 33-42.
+ *
+ * <p>This tree layout is intended to be extended (see {@link pv.Mark#extend})
+ * by a {@link pv.Bar}. The data property returns an array of nodes for use by
+ * other property functions. The following node attributes are supported:
+ *
+ * <ul>
+ * <li><tt>left</tt> - the cell left position.
+ * <li><tt>top</tt> - the cell top position.
+ * <li><tt>width</tt> - the cell width.
+ * <li><tt>height</tt> - the cell height.
+ * <li><tt>depth</tt> - the node depth (tier; the root is 0).
+ * <li><tt>keys</tt> - an array of string keys for the node.
+ * <li><tt>size</tt> - the aggregate node size.
+ * <li><tt>children</tt> - child nodes, if any.
+ * <li><tt>data</tt> - the associated tree element, for leaf nodes.
+ * </ul>
+ *
+ * To produce a default treemap layout, say:
+ *
+ * <pre>.add(pv.Bar)
+ *   .extend(pv.Layout.treemap(tree))</pre>
+ *
+ * To display internal nodes, and color by depth, say:
+ *
+ * <pre>.add(pv.Bar)
+ *   .extend(pv.Layout.treemap(tree).inset(10))
+ *   .fillStyle(pv.Colors.category19().by(function(n) n.depth))</pre>
+ *
+ * The format of the <tt>tree</tt> argument is a hierarchical object whose leaf
+ * nodes are numbers corresponding to their size. For an example, and
+ * information on how to convert tabular data into such a tree, see
+ * {@link pv.Tree}. If the leaf nodes are not numbers, a {@link #size} function
+ * can be specified to override how the tree is interpreted. This size function
+ * can also be used to transform the data.
+ *
+ * <p>By default, the treemap fills the full width and height of the parent
+ * panel, and only leaf nodes are rendered. If an {@link #inset} is specified,
+ * internal nodes will be rendered, each inset from their parent by the
+ * specified margins. Rounding can be enabled using {@link #round}. Finally, an
+ * optional root key can be specified using {@link #root} for convenience.
+ *
+ * @param tree a tree (an object) who leaf attributes have sizes.
+ * @returns {pv.Layout.treemap} a tree layout.
+ */
+pv.Layout.treemap = function(tree) {
+  var keys = [], round, inset, sizeof = Number;
+
+  /** @private */
+  function rnd(i) {
+    return round ? Math.round(i) : i;
+  }
+
+  /** @private */
+  function accumulate(map) {
+    var node = {size: 0, children: [], keys: keys.slice()};
+    for (var key in map) {
+      var child = map[key], size = sizeof(child);
+      keys.push(key);
+      if (isNaN(size)) {
+        child = accumulate(child);
+      } else {
+        child = {size: size, data: child, keys: keys.slice()};
+      }
+      node.children.push(child);
+      node.size += child.size;
+      keys.pop();
+    }
+    node.children.sort(function(a, b) { return a.size - b.size; });
+    return node;
+  }
+
+  /** @private */
+  function scale(node, k) {
+    node.size *= k;
+    if (node.children) {
+      for (var i = 0; i < node.children.length; i++) {
+        scale(node.children[i], k);
+      }
+    }
+  }
+
+  /** @private */
+  function ratio(row, l) {
+    var rmax = -Infinity, rmin = Infinity, s = 0;
+    for (var i = 0; i < row.length; i++) {
+      var r = row[i].size;
+      if (r < rmin) rmin = r;
+      if (r > rmax) rmax = r;
+      s += r;
+    }
+    s = s * s;
+    l = l * l;
+    return Math.max(l * rmax / s, s / (l * rmin));
+  }
+
+  /** @private */
+  function squarify(node) {
+    var row = [], mink = Infinity;
+    var x = node.left + (inset ? inset.left : 0),
+        y = node.top + (inset ? inset.top : 0),
+        w = node.width - (inset ? inset.left + inset.right : 0),
+        h = node.height - (inset ? inset.top + inset.bottom : 0),
+        l = Math.min(w, h);
+
+    scale(node, w * h / node.size);
+
+    function position(row) {
+      var s = pv.sum(row, function(node) { return node.size; }),
+          hh = (l == 0) ? 0 : rnd(s / l);
+
+      for (var i = 0, d = 0; i < row.length; i++) {
+        var n = row[i], nw = rnd(n.size / hh);
+        if (w == l) {
+          n.left = x + d;
+          n.top = y;
+          n.width = nw;
+          n.height = hh;
+        } else {
+          n.left = x;
+          n.top = y + d;
+          n.width = hh;
+          n.height = nw;
+        }
+        d += nw;
+      }
+
+      if (w == l) {
+        if (n) n.width += w - d; // correct rounding error
+        y += hh;
+        h -= hh;
+      } else {
+        if (n) n.height += h - d; // correct rounding error
+        x += hh;
+        w -= hh;
+      }
+      l = Math.min(w, h);
+    }
+
+    var children = node.children.slice(); // copy
+    while (children.length > 0) {
+      var child = children[children.length - 1];
+      if (child.size <= 0) {
+        children.pop();
+        continue;
+      }
+      row.push(child);
+
+      var k = ratio(row, l);
+      if (k <= mink) {
+        children.pop();
+        mink = k;
+      } else {
+        row.pop();
+        position(row);
+        row.length = 0;
+        mink = Infinity;
+      }
+    }
+
+    if (row.length > 0) {
+      position(row);
+    }
+
+    /* correct rounding error */
+    if (w == l) {
+      for (var i = 0; i < row.length; i++) {
+        row[i].width += w;
+      }
+    } else {
+      for (var i = 0; i < row.length; i++) {
+        row[i].height += h;
+      }
+    }
+  }
+
+  /** @private */
+  function layout(node) {
+    if (node.children) {
+      squarify(node);
+      for (var i = 0; i < node.children.length; i++) {
+        var child = node.children[i];
+        child.depth = node.depth + 1;
+        layout(child);
+      }
+    }
+  }
+
+  /** @private */
+  function flatten(node, array) {
+    if (node.children) {
+      for (var i = 0; i < node.children.length; i++) {
+        flatten(node.children[i], array);
+      }
+    }
+    if (inset || !node.children) {
+      array.push(node)
+    }
+    return array;
+  }
+
+  /** @private */
+  function data() {
+    var root = accumulate(tree);
+    root.left = 0;
+    root.top = 0;
+    root.width = this.parent.width();
+    root.height = this.parent.height();
+    root.depth = 0;
+    layout(root);
+    return flatten(root, []).reverse();
+  }
+
+  /* A dummy mark, like an anchor, which the caller extends. */
+  var mark = new pv.Mark()
+      .data(data)
+      .left(function(n) { return n.left; })
+      .top(function(n) { return n.top; })
+      .width(function(n) { return n.width; })
+      .height(function(n) { return n.height; });
+
+  /**
+   * Enables or disables rounding. When rounding is enabled, the left, top,
+   * width and height properties will be rounded to integer pixel values. The
+   * rounding algorithm uses error accumulation to ensure an exact fit.
+   *
+   * @param {boolean} v whether rounding should be enabled.
+   * @function
+   * @name pv.Layout.treemap.prototype.round
+   * @returns {pv.Layout.treemap} this.
+   */
+  mark.round = function(v) {
+    round = v;
+    return this;
+  };
+
+  /**
+   * Specifies the margins to inset child nodes from their parents; as a side
+   * effect, this also enables the display of internal nodes, which are hidden
+   * by default. If only a single argument is specified, this value is used to
+   * inset all four sides.
+   *
+   * @param {number} top the top margin.
+   * @param {number} [right] the right margin.
+   * @param {number} [bottom] the bottom margin.
+   * @param {number} [left] the left margin.
+   * @function
+   * @name pv.Layout.treemap.prototype.inset
+   * @returns {pv.Layout.treemap} this.
+   */
+  mark.inset = function(top, right, bottom, left) {
+    if (arguments.length == 1) right = bottom = left = top;
+    inset = {top:top, right:right, bottom:bottom, left:left};
+    return this;
+  };
+
+  /**
+   * Specifies the root key; optional. The root key is prepended to the
+   * <tt>keys</tt> attribute for all generated nodes. This method is provided
+   * for convenience and does not affect layout.
+   *
+   * @param {string} v the root key.
+   * @function
+   * @name pv.Layout.treemap.prototype.root
+   * @returns {pv.Layout.treemap} this.
+   */
+  mark.root = function(v) {
+    keys = [v];
+    return this;
+  };
+
+  /**
+   * Specifies the sizing function. By default, the sizing function is
+   * <tt>Number</tt>. The sizing function is invoked for each node in the tree
+   * (passed to the constructor): the sizing function must return
+   * <tt>undefined</tt> or <tt>NaN</tt> for internal nodes, and a number for
+   * leaf nodes. The aggregate sizes of internal nodes will be automatically
+   * computed by the layout.
+   *
+   * <p>For example, if the tree data structure represents a file system, with
+   * files as leaf nodes, and each file has a <tt>bytes</tt> attribute, you can
+   * specify a size function as:
+   *
+   * <pre>.size(function(d) d.bytes)</pre>
+   *
+   * This function will return <tt>undefined</tt> for internal nodes (since
+   * these do not have a <tt>bytes</tt> attribute), and a number for leaf nodes.
+   *
+   * <p>Note that the built-in <tt>Math.sqrt</tt> and <tt>Math.log</tt> methods
+   * can be used as sizing functions. These function similarly to
+   * <tt>Number</tt>, except perform a root and log scale, respectively.
+   *
+   * @param {function} f the new sizing function.
+   * @function
+   * @name pv.Layout.treemap.prototype.size
+   * @returns {pv.Layout.treemap} this.
+   */
+  mark.size = function(f) {
+    sizeof = f;
+    return this;
+  };
+
+  return mark;
+};
+ return pv;}();/*
+ * Parses the Protovis specifications on load, allowing the use of JavaScript
+ * 1.8 function expressions on browsers that only support JavaScript 1.6.
+ *
+ * @see pv.parse
+ */
+pv.listen(window, "load", function() {
+    var scripts = document.getElementsByTagName("script");
+    for (var i = 0; i < scripts.length; i++) {
+      var s = scripts[i];
+      if (s.type == "text/javascript+protovis") {
+        try {
+          pv.Panel.$dom = s;
+          window.eval(pv.parse(s.textContent || s.innerHTML)); // IE
+        } catch (e) {
+          pv.error(e);
+        }
+        delete pv.Panel.$dom;
+      }
+    }
+  });