docs: function (xhr, message, callback) {
          var response;
  
          switch (xhr.status) {
              case this.RESPONSE_OK:
                  response = JSON.parse(xhr.responseText);
                  break;
              case this.RESPONSE_UNPROCESSABLE_ENTITY:
                  response = JSON.parse(xhr.responseText);
                  break;
              case this.RESPONSE_NOT_FOUND:
                  response = {
                    error : xhr.status
                  };
                  break;
              case this.RESPONSE_INTERNAL_SERVER_ERROR:
                  response = {};
                  break;
              case this.RESPONSE_SERVER_UNAVALIABLE:
                  console.log('Server is unavailable, probably shutdown.');
                  response = {};
                  break;
              default:
                  console.log('Unsuported code returned from the server: ', xhr.status);
                  response = {
                      error : xhr.status
                  };
          }
  
          callback(response);
  
          return this;
      }