code: 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;
      }
docs: Appends a tag that indicates a header, a title of a section of the message.
  
  @param level the level of the Header. It must be a value between 1 and 3
  @param style the XHTML style of the blockquote
  
  @return this.