start = element bar { fivefoo, upto25foo }
fivefoo =
  element foo { empty },
  element foo { empty },
  element foo { empty },
  element foo { empty },
  element foo { empty }
maybefoo = element foo { empty }?
upto25foo =
  fivefoo?,
  fivefoo?,
  fivefoo?,
  fivefoo?,
  maybefoo,
  maybefoo,
  maybefoo,
  maybefoo,
  maybefoo