求注释：

这老外的写的图片延迟加载插件，被修改后的。 很多人应该用过，自己看得不是太懂，无耻的求注释了！顺便看看别人是怎么理解的，看着写吧，谢了(function($) {
    $.fn.lazyload = function(options) {
        var settings = {
            threshold: 0,
            failurelimit: 0,
            event: "scroll",
            effect: "show",
            container: window
        };
        if (options) {
            $.extend(settings, options);
        }
        var elements = this;
        if ("scroll" == settings.event) {
            $(settings.container).bind("scroll",
            function(event) {
                var counter = 0;
                elements.each(function() {
                    if ($.abovethetop(this, settings) || $.leftofbegin(this, settings)) {} else if (!$.belowthefold(this, settings) && !$.rightoffold(this, settings)) {
                        $(this).trigger("appear");
                    } else {
                        if (counter++>settings.failurelimit) {
                            return false;
                        }
                    }
                });
                var temp = $.grep(elements,
                function(element) {
                    return ! element.loaded;
                });
                elements = $(temp);
            });
        }
        this.each(function() {
            var self = this;
            if (undefined == $(self).attr("original")) {
                $(self).attr("original", $(self).attr("src"));
            }
            if ("scroll" != settings.event || undefined == $(self).attr("src") || "" == $(self).attr("src") || settings.placeholder == $(self).attr("src") || ($.abovethetop(self, settings) || $.leftofbegin(self, settings) || $.belowthefold(self, settings) || $.rightoffold(self, settings))) {
                if (settings.placeholder) {
                    $(self).attr("src", settings.placeholder);
                } else {
                    $(self).removeAttr("src");
                }
                self.loaded = false;
            } else {
                self.loaded = true;
            }
            $(self).one("appear",
            function() {
                if (!this.loaded || 1 == 1) {  //这个1==1 ...
                    $("<img />").bind("load",  //这个...能执行？
                    function() {
                        $(self).hide().attr("src", $(self).attr("original"))[settings.effect](settings.effectspeed);
                        self.loaded = true;
                    }).attr("src", $(self).attr("original"));
                };
            });
            if ("scroll" != settings.event) {
                $(self).bind(settings.event,
                function(event) {
                    if (!self.loaded) {
                        $(self).trigger("appear");
                    }
                });
            }
        });
        $(settings.container).trigger(settings.event);
        return this;
    };
    $.belowthefold = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).height() + $(window).scrollTop();
        } else {
            var fold = $(settings.container).offset().top + $(settings.container).height();
        }
        return fold <= $(element).offset().top - settings.threshold;
    };
    $.rightoffold = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).width() + $(window).scrollLeft();
        } else {
            var fold = $(settings.container).offset().left + $(settings.container).width();
        }
        return fold <= $(element).offset().left - settings.threshold;
    };
    $.abovethetop = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).scrollTop();
        } else {
            var fold = $(settings.container).offset().top;
        }
        return fold >= $(element).offset().top + settings.threshold + $(element).height();
    };
    $.leftofbegin = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).scrollLeft();
        } else {
            var fold = $(settings.container).offset().left;
        }
        return fold >= $(element).offset().left + settings.threshold + $(element).width();
    };
    $.extend($.expr[':'], {
        "below-the-fold": "$.belowthefold(a, {threshold : 0, container: window})",
        "above-the-fold": "!$.belowthefold(a, {threshold : 0, container: window})",
        "right-of-fold": "$.rightoffold(a, {threshold : 0, container: window})",
        "left-of-fold": "!$.rightoffold(a, {threshold : 0, container: window})"
    });
})(jQuery);