<div>

　　　　<div id="bar">
		<span>
			<a href="http://www.mamicode.com/###">asfd</a>
		</span>
	</div>

</div>

var bar = document.getElementById(‘bar‘);
console.log(bar.querySelectorAll(‘div span a‘).length); // 1 
console.log(bar.querySelectorAll(‘span a‘).length);  // 1
console.log($(‘div span a‘,bar)); // jQuery没有选择到

try {
                    /*
                     * This checking here is to "fix" the behaviour of querySelectorAll
                     * for non root document queries. The way qsa works is intentional,
                     * however it‘s definitely not the expected way it should work.
                     * When descendant selectors are used, only the lowest selector must be inside the root!
                     * More info: http://ejohn.org/blog/thoughts-on-queryselectorall/
                     * So we create a descendant selector by prepending the root‘s ID, and query the parent node.
                     * UNLESS the root has no parent in which qsa will work perfectly.
                     *
                     * We only modify the path for single selectors (ie, no multiples),
                     * without a full parser it makes it difficult to do this correctly.
                     */
　　　　　　　　　　　　// startIdRe = /^\s*#/;

                    if (root.parentNode && (root.nodeType !== 9) && path.indexOf(‘,‘) === -1 && !startIdRe.test(path)) {
                        path = ‘#‘ + Ext.escapeId(Ext.id(root)) + ‘ ‘ + path;
                        root = root.parentNode;
                    }
                    return single ? [ root.querySelector(path) ]
                        : Ext.Array.toArray(root.querySelectorAll(path));
                }
                catch (e) {
                }