/// What a search for a meaning matches in [gloss], lower case: the gloss
/// without its remarks in brackets, and without a leading "to" or article
/// too (`to eat` gives `to eat` and `eat`; `the sun (in the sky)` gives
/// `the sun` and `sun`). Empty for a gloss of remarks only.
List<String> glossKeys(String gloss) {
  final plain = gloss
      .toLowerCase()
      .replaceAll(RegExp(r'\([^)]*\)'), ' ')
      .replaceAll(RegExp(r'\s+'), ' ')
      .trim();
  if (plain.isEmpty) {
    return const [];
  }
  final bare = plain.replaceFirst(RegExp('^(to|a|an|the) '), '');
  return {plain, bare}.toList();
}