code: function propagate (parent, prefix) {
  	var self = this;
  
  	if (!parent || typeof parent.emit !== 'function') {
  		throw new TypeError('"parent" argument must implement an "emit" method');
  	}
  
  	self.parent = parent;
  	self.parentPrefix = prefix;
  
  	return this;
  }
docs: Adds the parent eventemitter to the end of the bubblers array.
  When this eventemitter has emitted an event it will emit the same event on the parent.
  
  This function is namespaced under 'EventEmitter' because it's usually not part of what
  people perceive as an event emitter.
  
  @param  {EventEmitter} parent   The eventemitter to propagate events to.
  @param  {String}       prefix   Optional prefix for the eventName, like 'user-' => user-logout.
  @return {Object}                `this`-object.