docs: function highlightCode(highlight, $) {
      return editHTMLElement($, 'code', function($code) {
          var classNames = ($code.attr('class') || '').split(' ');
          var lang = getLanguageForClass(classNames);
          var source = $code.text();
  
          return Promise(highlight(lang, source))
          .then(function(r) {
              if (is.string(r.html)) {
                  $code.html(r.html);
              } else {
                  $code.text(r.text);
              }
          });
      });
  }