static Set<S> codeAnalysis_getUnknownIdentifiers(S code) {
  SS map = codeAnalysis_identifierSafetyMap();
  Set<S> identifiers = tok_allIdentifiers(code);
  
  new TreeSet<S> set;
  for (S id : identifiers) {
    if (!codeAnalysis_isSafeIdentifier(id)
      && (!map.containsKey(id) || contains(map.get(id), "?")))
        set.add(id);
  }
  
  ret set;
}