如何编写jquery表单验证插件？

Question

我想学习些一个jquery表单验证插件，已经写了一点，下面该如何完善呢？
(function ($) {
    $.extend({
        pluginname: function (options) { 
            var defaults = {
                username: { required: '请输入姓名',
                    minlength: 2,
                    tip:'请至少输入2个字符'
                },
                password: { required: '请输入姓名',
                    minlength: 2,
                    tip:'请至少输入2个字符'
                }
            }
            var options = $.extend(defaults, options);
             return this.each(function () {
                
            });
        }
    });
})(jQuery);