static Collection<S> getCodeFragmentSafety(S code) {
  SS map = codeAnalysis_identifierSafetyMap();
  Set<S> identifiers = tok_allIdentifiers(code);
  
  Collection<S> tags = treeSet();
  for (S id : identifiers) {
    S tag;
    if (codeAnalysis_isSafeIdentifier(id)) tag = "safe"; // dangerous functions don't start with $
    else tag = or2(map.get(id), "?");
    tags.addAll(tokSplitAtComma(tag));
  }
  
  tags = simplifySafetyTags(tags);
  if (empty(tags)) tags.add("safe");
  ret tags;
}