docs: function() {
      // Walk all of the elements in the DOM (try to only do this once)
      var elements = doc.getElementsByTagName('*');
      var re = /url\((http.*)\)/ig;
      for (var i = 0; i < elements.length; i++) {
        var el = elements[i];
        var style = win.getComputedStyle(el);
  
        // check for Images
        if (el.tagName == 'IMG') {
          CheckElement(el, el.src);
        }
        // Check for background images
        if (style['background-image']) {
          re.lastIndex = 0;
          var matches = re.exec(style['background-image']);
          if (matches && matches.length > 1)
            CheckElement(el, matches[1]);
        }
        // recursively walk any iFrames
        if (el.tagName == 'IFRAME') {
          try {
            var rect = GetElementViewportRect(el);
            if (rect) {
              var tm = RUMSpeedIndex(el.contentWindow);
              if (tm) {
                rects.push({'tm': tm,
                            'area': rect.area,
                            'rect': rect});
              }
          }
          } catch(e) {
          }
        }
      }
    }