Constructs an list of indexable phrases from the document.  List is in
order of frequency, partially weighted by number of words.

options:
  a : all phrases instead of 1/30 truncation
  h : filter html (automatic if url starts with 'http' or ends with 'htm?')
  o : filter html only; do not index
  s : arg is string, not filename
  v : vertical output
  w : weighted ordering instead of numeric
  W : web filter

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