原来选择器只支持一个上下文，并对IE8的BUG进行了规避

     if (!flag_xml && doc.querySelectorAll) {//FF,opera,chrome,safari的XML文档也实现了querySelectorAll接口，但不能用var query = expr;//IE的getElementsByTagName,querySelectorAll对OBJECT元素的孩子的查找都存在问题if( doc.documentMode === 8 && context.nodeType === 1 && context.nodeName.toLowerCase() !== "object"){var id = context.getAttribute( "id" ),uid = context.uniqueID//IE8在上下文为元素节时，搜索结果包含自己if ( !id ) {context.setAttribute( "id", uid );}try {return pushResult(context.querySelectorAll( "#" + uid + " " + query ),result,flag_multi);} catch(e) {} finally {if ( id == context.uniqueID ) {context.removeAttribute( "id" );}}}else{if(/\!\=/.test(query))//手动支持 E[Attr!=Val]query = query.replace(/\[\s*(\w+)\s*!=\s*((['"]*).*?\3)\s*\]/g,":not([$1=$2])");try {return pushResult( context.querySelectorAll(query) ,result,flag_multi);} catch(e) {}}}

改进如下，现在只需规避IE的OBJECT bug。

            if (!flag_xml && doc.querySelectorAll) {//http://www.w3.org/TR/selectors/node = context;//使用替身，以便在多上下文实现不重排查找var useContains = false;if(contexts.length > 2 || doc.documentMode === 8 && context.nodeType === 1){node = doc;useContains = true;}if(doc.documentMode !== 8  ||  node.nodeName.toLowerCase() !== "object"){try{nodes = pushResult( node.querySelectorAll(expr) ,result,flag_multi);var ret = []if(useContains && nodes.length){var cn = contexts.length;for(i = 0, ri = 0; i < nodes.length; i++){inner:for(var c = 0; c < cn; c++){if(dom.contains(contexts[c], nodes[i])){ret.push(nodes[i])break inner;}}}return ret;}return result;}catch(e){}}}

另一种改进是，通过对元素节点的上下文添加一个类名，这样查找就可以一步到位。不足之处就是前前后后要对类进行操作。

            if (!flag_xml && doc.querySelectorAll) {var query = expr;if(contexts.length > 2 || doc.documentMode == 8  && context.nodeType == 1  ){if(contexts.length > 2 )context = doc;query = ".fix_icarus_sqa "+query;//IE8也要使用类名确保查找范围for(i = 0; node = contexts[i++];){if(node.nodeType === 1){node.className = "fix_icarus_sqa " + node.className;}}}if(doc.documentMode !== 8  || context.nodeName.toLowerCase() !== "object"){try{result = pushResult( context.querySelectorAll(query) ,result,flag_multi);if(query.indexOf(".fix_icarus_sqa") === 0 ){//如果为上下文添加了类名，就要去类名for(i = 0; node = contexts[i++];){if(node.nodeType === 1){node.className =  node.className.replace(" fix_icarus_sqa","");}}}return result;}catch(e){}}}

但显然对类进行操作对调用dom.contains快捷得多了。