code: function steppingDispatch() {
          applyExternalEffect(options.stepping.effect);  // WARNING: may change `options.stepping.effect`
          var event = options.dequeue(events);
          if (!event) {
              return false;
          }
          var effect = options.stepping.effect;
          effect.event = event;
          try {
              var behavior = event.context.behavior;
              effect.behavior = behavior;
              event.context.behavior(event.message);  // execute actor behavior
              if (behavior !== event.context.behavior) {
                  effect.became = event.context.behavior;
              }
          } catch (exception) {
              effect.exception = exception;
          }
          applyBehaviorEffect(effect);  // WARNING: will change `options.stepping.effect`
          return effect;
      }
docs: /*
  Dispatch the next `event`.
  
  Return: _Effect_ or `false`. Effect of dispatching the next `event` or
  `false` if no events exists for dispatch.