static Collection<S> getCodeFragmentSafety(S code) {
  SS map = mechMap("JavaX Identifier Safety");
  Set<S> identifiers = tok_allIdentifiers(code);
  
  Collection<S> tags = treeSet();
  for (S id : identifiers) {
    S tag;
    if (startsWith(id, "$")) tag = "safe"; // assume it's a variable
    else tag = or2(map.get(id), "?");
    tags.addAll(tokSplitAtComma(tag));
  }
  
  tags = simplifySafetyTags(tags);
  if (empty(tags)) tags.add("?");
  ret tags;
}