code: function(elName, url, attr) {
           var node = this.createElementDefaultNS(elName);
           node.appendChild(this.write_wmc_OnlineResource(url));
           if (attr) {
               var optionalAttributes = ["width", "height", "format"];
               for (var i=0; i<optionalAttributes.length; i++) {
                   if (optionalAttributes[i] in attr) {
                       node.setAttribute(optionalAttributes[i], attr[optionalAttributes[i]]);
                   }
               }
           }
           return node;
       }
docs: Method: write_wmc_URLType
  Create a LogoURL/DescriptionURL/MetadataURL/DataURL/LegendURL node given a object and elementName.
  
  Parameters:
  elName - {String} Name of element (LogoURL/DescriptionURL/MetadataURL/LegendURL)
  url - {String} URL string value
  attr - {Object} Optional attributes (width, height, format)
  
  Returns:
  {Element} A WMC element node.