code: function(element) {
      var textLength = this._getInnerText(element).length;
      if (textLength === 0)
        return 0;
  
      var linkLength = 0;
  
      // XXX implement _reduceNodeList?
      this._forEachNode(element.getElementsByTagName("a"), function(linkNode) {
        linkLength += this._getInnerText(linkNode).length;
      });
  
      return linkLength / textLength;
    }
docs: Get the density of links as a percentage of the content
  This is the amount of text that is inside a link divided by the total text in the node.
  
  @param Element
  @return number (float)