docs: function(deferred, description, err) {
  
        // **EVENT:** the `step:error` event is emitted with the step description object and the error message if a step fails.
        this.emit('step:error', description, err);
  
        // **EVENT:** the `scenario:error` event is emitted with the error message if the scenario is interrupted.
        this.emit('scenario:error', err);
  
        deferred.reject(err);
      }