gistfile1.txt

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.js" type="text/javascript" charset="utf-8"></script>
<script type="text/javascript" charset="utf-8">
// jquery error checking plugin
(function($) {
	errors = {
		test: function() {
			var args = $.makeArray(arguments);
			var msg, test = args.shift();
			if ( msg = errors.tests[test].apply(this, args) ) throw msg;
		},
		tests: {
			classNameFormat: function (a) { return !a.match(/^\./) || 'jQuery: Incorrect leading dot in class name: '+a; }
		}
	};
	
	$.fn.extend({
		_addClass: $.fn.addClass,
		addClass: function(value) {
			errors.test('classNameFormat', value);
			return this._addClass.apply(this, arguments);
		}
	});
})(jQuery);

jQuery(function($) {
	$('body').addClass('.red');
	$('body').addClass('red');
});
</script>