docs: function(paramString, urls) {
          var product = 1;
          for (var i=0, len=paramString.length; i<len; i++) { 
              product *= paramString.charCodeAt(i) * this.URL_HASH_FACTOR; 
              product -= Math.floor(product); 
          }
          return urls[Math.floor(product * urls.length)];
      }