static bool startsWithWord(S a, S b, Matches m) {
  if (!endsWithLetterOrDigit(b)) b += " ";
  if (!startsWithIC(a, b)) false;
  if (m != null) m.m = new S[] {trim(substring(a, l(b)))};
  true;
}

static bool startsWithWord(S a, S b) {
  ret startsWithWord(a, b, null);
}