jQuery.fn.visible = function() {
	return this.css('visibility', 'visible');
};

jQuery.fn.invisible = function() {
	return this.css('visibility', 'hidden');
};

jQuery.fn.visibilityToggle = function() {
	return this.css('visibility', function(i, visibility) {
		return (visibility == 'visible') ? 'hidden' : 'visible';
	});
};