// returns a prefiltered list of elements; you still need to do a
// full-text search on those.
static <A> Cl<A> wordIndex_lookupString(WordIndex<A> index, S query) {
  L<IntRange> ranges = index.wordRanges(query);
  new Lowest<Cl<A>> best;
  
  for (IntRange r : ranges) {
    S word = substring(query, r);
    Cl<A> l;
    if (r.start == 0)
      l = endingWithIC(index.words(), word);
    else if (r.end == l(query))
      l = startingWithIC(index.words(), word);
    else
      l = index.get(word);
    best.put(l, l(l));
  }
  ret best!;
}