code: function(obj, event, callback) {
  		// Use jQuery to handle DOM events.
  		if(underscore.isElement(obj) && $){return $(obj).one(event, callback); }
  
  		// Turn the callback into a callback that will remove itself after getting execute.
  		var removeEvent = function() { underscore.off(obj, event, callback); };
  		callback = underscore.compose(removeEvent, callback);
  
  		// Register the self-removing callback normally.
  		this.on(obj, event, callback);
  	}
docs: ### once*([object, ]event, callback)* Register a function that will be called a single time when the event is published.