code: public static HtmlTree HEADING(HtmlTag headingTag, HtmlStyle styleClass, Content body) {
          return HEADING(headingTag, false, styleClass, body);
      }
docs: Generates a heading tag (h1 to h6) with style class attribute. It also encloses
  a content.
  
  @param headingTag the heading tag to be generated
  @param styleClass stylesheet class for the tag
  @param body content for the tag
  @return an HtmlTree object for the tag