/* Custom selectors for your convenience.  译: 提供自定义选择方便你使用。 */
/* Use as $("img:below-the-fold").something() or 译: 你可以这样使用 $("img:below-the-fold").something() 或 */
/* $("img").filter(":below-the-fold").something() which is faster 译: $("img").filter(":below-the-fold").something() 这样更快 */
// 简单翻译了下不知道准不准确。。
$.extend($.expr[":"], {"below-the-fold" : function(a) { return $.belowthefold(a, {threshold : 0}); },"above-the-top"  : function(a) { return !$.belowthefold(a, {threshold : 0}); },"right-of-screen": function(a) { return $.rightoffold(a, {threshold : 0}); },"left-of-screen" : function(a) { return !$.rightoffold(a, {threshold : 0}); },"in-viewport"    : function(a) { return $.inviewport(a, {threshold : 0}); },/* Maintain BC for couple of versions. */"above-the-fold" : function(a) { return !$.belowthefold(a, {threshold : 0}); },"right-of-fold"  : function(a) { return $.rightoffold(a, {threshold : 0}); },"left-of-fold"   : function(a) { return !$.rightoffold(a, {threshold : 0}); }
});

$.expr[':'].test = function(obj, index, meta, stack) {/* obj   - is a current DOM element 当前DOM元素index - the current loop index in stack 当前元素在stack中的索引，meta  - meta data about your selector !!! 用来存参数值，详见带参数的自定义选择器。stack - stack of all elements to loop 选择器所选中的元素集。Return true to include current element 返回 true 就包含当前元素Return false to explude current element 返回 false 就抛弃当前元素*/
};

$('.someClasses:test').doSomething();

$('.someClasses:test(argument)').doSomething();
$('.someClasses:test("arg1, arg2")').doSomething();
$(".someClasses:test('arg1, arg2')").doSomething();

$('.someClasses:test(argument)').doSomething();

[':test(argument)', // full selector 整个自定义选择器'test',            // only selector 自定义选择器名称'',                // quotes used   使用了什么引号(很明显这里没有)'argument'         // parameters    参数
]

$('.someClasses:test("arg1, arg2")').doSomething();

[':test("arg1, arg2")', // full selector 整个自定义选择器'test',                // only selector 自定义选择器名称'"',                   // quotes used   使用了什么引号(这里用的是双引号)'arg1, arg2'           // parameters    参数
]

$("a:test(haha)");

$.expr[':'].test = function(obj, index, meta, stack) {var txt = obj.innerHTML,key = meta[3];return txt.indexOf(key) > -1;
};
// 测试
$('#navList a:test(JavaScript)').each(function () {console.log(this.innerHTML);
});