docs: function executeEventHandlersSerially(hook, opts) {
      var handlers = events.listeners(hook);
      if (handlers.length) {
          // Chain the handlers in series.
          return handlers.reduce(function(soFar, f) {
              return soFar.then(function() { return f(opts); });
          }, Q());
      } else {
          return Q(); // Nothing to do.
      }
  }