docs: public XHTMLText appendOpenHeaderTag(int level, String style) {
          if (level > 3 || level < 1) {
              throw new IllegalArgumentException("Level must be between 1 and 3");
          }
          text.halfOpenElement(H + Integer.toString(level));
          text.optAttribute(STYLE, style);
          text.rightAngleBracket();
          return this;
      }