code: function (headerText, prevToken) {
          if (prevToken && prevToken.type === 'paragraph' && utils.isHtml(prevToken.text)) {
              var anchorFromHtml = utils.getAnchorFromHtml(prevToken.text);
              if (anchorFromHtml) {
                  return anchorFromHtml;
              }
          }
  
          var anchor = utils.getAnchorFromHeader(headerText, prevToken);
  
          if (this._cache.hasOwnProperty(anchor)) {
              anchor += '-' + this._cache[anchor]++;
          } else {
              this._cache[anchor] = 1;
          }
  
          return anchor;
      }
docs: Returns an anchor for a given header
  @param {String} headerText
  @returns {String}