docs: public static boolean checkOpenTagClosesOptional(TagName openTag, TagName optionalOpenTag) {
      checkArgument(optionalOpenTag.isDefinitelyOptional(), "Open tag is not optional.");
      if (!(openTag.isStatic() && optionalOpenTag.isStatic())) {
        return false;
      }
      String optionalTagName = optionalOpenTag.getStaticTagNameAsLowerCase();
      String openTagName = openTag.getStaticTagNameAsLowerCase();
      return OPTIONAL_TAG_OPEN_CLOSE_RULES.containsEntry(optionalTagName, openTagName);
    }