哪位高手能给小弟我简单分析下这个jQuery Validation插件，黄色部分看不懂为什么这么写

谁能给我简单分析下这个jQuery Validation插件，黄色部分看不懂为什么这么写？
nameAvailable: {
    check: function(value) {

        if (value) {
            var dataString = 'username=' + value;
            var result;

            // Checking availability...
            // Loads checking image.
            $(".availability_status").html('<img src="loader.gif" align="absmiddle">');
            
            // Sends ajax request to check the name is available or not.
            $.ajax({
                type: "GET",
                url: "UserService.ashx",
                data: dataString,
                success: function(data) {
                    
                    // When the checking completed, then loaded corresponding css style.
                    $('.availability_status').ajaxComplete(function(event, request, settings) {
                        if (data == false) {
                            $('.availability_status').html('');
                            $('.availability_status').removeClass('tick');
                            $('.availability_status').addClass('error');
                            return true;
                        }
                        else {
                            $('.availability_status').html('');
                            $('.availability_status').removeClass('error');
                            $('.availability_status').addClass('tick');

                            return false;
                        }
                    });

                }
            });

            // Sends a asyn reqeust, return false temporary.
            return false;
            ////                        e.preventDefault();
        }
        else {
            $('.availability_status').removeClass('tick');
            $('.availability_status').removeClass('error');
            return false;
        }
    },