### on*([object, ]event, callback)* Register a function to get called when a certain event is published. Any event handlers attached after an event has been triggered at least once will immediately be called with the most recently triggered value.
function(obj, event, callback) {
		// Use jQuery to handle DOM events.
		if(underscore.isElement(obj) && $){return $(obj).on(event, callback); }

		// Use internal handler for pubsub
		if(this.isString(obj)) {callback = event; event = obj; obj = this; }

		// Ensure a container is available for all events.
		if(!this.isObject(obj.__event_handlers)){ obj.__event_handlers = {}; }
		// Ensure a handler is available for this particular event.
		if (!(event in obj.__event_handlers)) {
			// Using a memory callback
			obj.__event_handlers[event] = underscore.Callbacks("memory");
		}
		obj.__event_handlers[event].add(callback);
		return this;
	}