code: public static HtmlTree META(String httpEquiv, String content, String charSet) {
          HtmlTree htmltree = new HtmlTree(HtmlTag.META);
          String contentCharset = content + "; charset=" + charSet;
          htmltree.addAttr(HtmlAttr.HTTP_EQUIV, nullCheck(httpEquiv));
          htmltree.addAttr(HtmlAttr.CONTENT, contentCharset);
          return htmltree;
      }
docs: Generates a META tag with the http-equiv, content and charset attributes.
  
  @param httpEquiv http equiv attribute for the META tag
  @param content type of content
  @param charSet character set used
  @return an HtmlTree object for the META tag