code: function()  {
          for (var i=0, len=this.renderers.length; i<len; i++) {
              var rendererClass = this.renderers[i];
              var renderer = (typeof rendererClass == "function") ?
                  rendererClass :
                  OpenLayers.Renderer[rendererClass];
              if (renderer && renderer.prototype.supported()) {
                  this.renderer = new renderer(this.div, this.rendererOptions);
                  break;
              }  
          }  
      }
docs: Method: assignRenderer
  Iterates through the available renderer implementations and selects
  and assigns the first one whose "supported()" function returns true.