static void keepOnlyCommentedScreenClips(bool doIt) {
  Set<S> md5s = new HashSet(keys(thingsOnScreenDefinitions()));
  aggressivelyCollectPossibleMD5sInTextFile(glyphTeachLog(), md5s);
    
  for (File f : filesEndingWith(screenClipsDir(), ".png"))
    if (!md5s.contains(toLower(dropSuffix(".png", f.getName()))))
      if (doIt)
        moveFileToDirVerbose(f, javaxCachesDir("Deleted Screen Clips"));
      else
        print("Would delete " + f2s(f));
}