code: function _readyState(o, c) {
          if (o.c.readyState === 4) {
              if (c.timeout) {
                  _clearTimeout(o.id);
              }
  
              w.setTimeout(
                  function() {
                      _ioComplete(o, c);
                      _handleResponse(o, c);
                  }, 0);
          }
      }
docs: @description Event handler bound to onreadystatechange.
  
  @method _readyState
  @private
  @static
  @param {object} o - Transaction object generated by _create().
  @param {object} c - Configuration object passed to YUI.io().
  @return void