//兼容性，support是做兼容性检测，检测完之后实施是通过钩子机制。jQuery.support = (function( support ) {
   //右边函数会立即执行    var input = document.createElement("input"),        fragment = document.createDocumentFragment(),//文档碎片        div = document.createElement("div"),        select = document.createElement("select"),        opt = select.appendChild( document.createElement("option") );    // input.type默认是text,基本都有，    if ( !input.type ) {        return support;    }    //改成复选框    input.type = "checkbox";    //新版本value的值是'on',老版本value的值是'',所以新本版support.checkOn=true,老版本support.checkOn=false,就可以通过support.checkOn属性值进行浏览器类型判断。    support.checkOn = input.value !== "";    // 狐火chrome下拉子项默认是选中的，ie默认不选中。    support.optSelected = opt.selected;    // 定义初始值    support.reliableMarginRight = true;    support.boxSizingReliable = true;    support.pixelPosition = false;    // Make sure checked status is properly cloned    // Support: IE9, IE10    //先让input选中，然后克隆，再判断选中状态，火狐chromeIE10以上都是选中的，ie低版本不是选中。    input.checked = true;    support.noCloneChecked = input.cloneNode( true ).checked;    // Make sure that the options inside disabled selects aren't marked as disabled    // (WebKit marks them as disabled)    //下拉菜单禁止，子项有没有禁止。    select.disabled = true;    support.optDisabled = !opt.disabled;    // Check if an input maintains its value after becoming a radio    // Support: IE9, IE10    input = document.createElement("input");    input.value = "t";    input.type = "radio";    support.radioValue = input.value === "t";    // #11217 - WebKit loses check when the name is after the checked attribute    input.setAttribute( "checked", "t" );    input.setAttribute( "name", "t" );    fragment.appendChild( input );    // Support: Safari 5.1, Android 4.x, Android 2.3    // old WebKit doesn't clone checked state correctly in fragments    support.checkClone = fragment.cloneNode( true ).cloneNode( true ).lastChild.checked;    // Support: Firefox, Chrome, Safari    // Beware of CSP restrictions (https://developer.mozilla.org/en/Security/CSP)    support.focusinBubbles = "onfocusin" in window;    //首先定义一个div的背景剪切是内容剪切，然后复制一份设置背景剪切为空，然后看原来div的背景剪切还是不是内容剪切。    div.style.backgroundClip = "content-box";    div.cloneNode( true ).style.backgroundClip = "";    support.clearCloneStyle = div.style.backgroundClip === "content-box";    //下面的需要等dom加载完才能检测    jQuery(function() {        var container, marginDiv,            // Support: Firefox, Android 2.3 (Prefixed box-sizing versions).            //            divReset = "padding:0;margin:0;border:0;display:block;-webkit-box-sizing:content-box;-moz-box-sizing:content-box;box-sizing:content-box",            body = document.getElementsByTagName("body")[ 0 ];        if ( !body ) {            // Return for frameset docs that don't have a body            return;        }        //创建一个container来检测        container = document.createElement("div");        container.style.cssText = "border:0;width:0;height:0;position:absolute;top:0;left:-9999px;margin-top:1px";        // Check box-sizing and margin behavior.        body.appendChild( container ).appendChild( div );        div.innerHTML = "";        // Support: Firefox, Android 2.3 (Prefixed box-sizing versions).        div.style.cssText = "-webkit-box-sizing:border-box;-moz-box-sizing:border-box;box-sizing:border-box;padding:1px;border:1px;display:block;width:4px;margin-top:1%;position:absolute;top:1%";        // Workaround failing boxSizing test due to offsetWidth returning wrong value        // with some non-1 values of body zoom, ticket #13543        jQuery.swap( body, body.style.zoom != null ? { zoom: 1 } : {}, function() {            support.boxSizing = div.offsetWidth === 4;        });        // Use window.getComputedStyle because jsdom on node.js will break without it.        if ( window.getComputedStyle ) {            support.pixelPosition = ( window.getComputedStyle( div, null ) || {} ).top !== "1%";            support.boxSizingReliable = ( window.getComputedStyle( div, null ) || { width: "4px" } ).width === "4px";            // Support: Android 2.3            // Check if div with explicit width and no margin-right incorrectly            // gets computed margin-right based on width of container. (#3333)            // WebKit Bug 13343 - getComputedStyle returns wrong value for margin-right            marginDiv = div.appendChild( document.createElement("div") );            marginDiv.style.cssText = div.style.cssText = divReset;            marginDiv.style.marginRight = marginDiv.style.width = "0";            div.style.width = "1px";            support.reliableMarginRight =                !parseFloat( ( window.getComputedStyle( marginDiv, null ) || {} ).marginRight );        }        body.removeChild( container );    });    return support;//返回json})( {} );//实参json