private static String getTagName(@Nullable String tag) {
      if (tag == null) return null;
      int start = -1;
      for (int i = 0; i < tag.length(); i ++) {
        char c = tag.charAt(i);
        if (Character.isAlphabetic(c)) {
          if (start < 0)
            start = i;
        }
        else {
          if (start >= 0)
            return tag.substring(start, i);
        }
      }
      return start >= 0 ? tag.substring(start) : null;
    }
private static String getTagName(@Nullable String tag)