function child(p, index){
        var i = 0,
        	n = p.firstChild;
        while(n){
            if(n.nodeType == 1){
               if(++i == index){
                   return n;
               }
            }
            n = n.nextSibling;
        }
        return null;
    }
@class Ext.DomQuery
Provides high performance selector/xpath processing by compiling queries into reusable functions. New pseudo classes and matchers can be plugged. It works on HTML and XML documents (if a content node is passed in).
<p>
DomQuery supports most of the <a href="http://www.w3.org/TR/2005/WD-css3-selectors-20051215/#selectors">CSS3 selectors spec</a>, along with some custom selectors and basic XPath.</p>

<p>
All selectors, attribute filters and pseudos below can be combined infinitely in any order. For example "div.foo:nth-child(odd)[@foo=bar].bar:first" would be a perfectly valid selector. Node filters are processed in the order in which they appear, which allows you to optimize your queries for your document structure.
</p>
<h4>Element Selectors:</h4>
<ul class="list">
    <li> <b>*</b> any element</li>
    <li> <b>E</b> an element with the tag E</li>
    <li> <b>E F</b> All descendent elements of E that have the tag F</li>
    <li> <b>E > F</b> or <b>E/F</b> all direct children elements of E that have the tag F</li>
    <li> <b>E + F</b> all elements with the tag F that are immediately preceded by an element with the tag E</li>
    <li> <b>E ~ F</b> all elements with the tag F that are preceded by a sibling element with the tag E</li>
</ul>
<h4>Attribute Selectors:</h4>
<p>The use of &#64; and quotes are optional. For example, div[&#64;foo='bar'] is also a valid attribute selector.</p>
<ul class="list">
    <li> <b>E[foo]</b> has an attribute "foo"</li>
    <li> <b>E[foo=bar]</b> has an attribute "foo" that equals "bar"</li>
    <li> <b>E[foo^=bar]</b> has an attribute "foo" that starts with "bar"</li>
    <li> <b>E[foo$=bar]</b> has an attribute "foo" that ends with "bar"</li>
    <li> <b>E[foo*=bar]</b> has an attribute "foo" that contains the substring "bar"</li>
    <li> <b>E[foo%=2]</b> has an attribute "foo" that is evenly divisible by 2</li>
    <li> <b>E[foo!=bar]</b> has an attribute "foo" that does not equal "bar"</li>
</ul>
<h4>Pseudo Classes:</h4>
<ul class="list">
    <li> <b>E:first-child</b> E is the first child of its parent</li>
    <li> <b>E:last-child</b> E is the last child of its parent</li>
    <li> <b>E:nth-child(<i>n</i>)</b> E is the <i>n</i>th child of its parent (1 based as per the spec)</li>
    <li> <b>E:nth-child(odd)</b> E is an odd child of its parent</li>
    <li> <b>E:nth-child(even)</b> E is an even child of its parent</li>
    <li> <b>E:only-child</b> E is the only child of its parent</li>
    <li> <b>E:checked</b> E is an element that is has a checked attribute that is true (e.g. a radio or checkbox) </li>
    <li> <b>E:first</b> the first E in the resultset</li>
    <li> <b>E:last</b> the last E in the resultset</li>
    <li> <b>E:nth(<i>n</i>)</b> the <i>n</i>th E in the resultset (1 based)</li>
    <li> <b>E:odd</b> shortcut for :nth-child(odd)</li>
    <li> <b>E:even</b> shortcut for :nth-child(even)</li>
    <li> <b>E:contains(foo)</b> E's innerHTML contains the substring "foo"</li>
    <li> <b>E:nodeValue(foo)</b> E contains a textNode with a nodeValue that equals "foo"</li>
    <li> <b>E:not(S)</b> an E element that does not match simple selector S</li>
    <li> <b>E:has(S)</b> an E element that has a descendent that matches simple selector S</li>
    <li> <b>E:next(S)</b> an E element whose next sibling matches simple selector S</li>
    <li> <b>E:prev(S)</b> an E element whose previous sibling matches simple selector S</li>
</ul>
<h4>CSS Value Selectors:</h4>
<ul class="list">
    <li> <b>E{display=none}</b> css value "display" that equals "none"</li>
    <li> <b>E{display^=none}</b> css value "display" that starts with "none"</li>
    <li> <b>E{display$=none}</b> css value "display" that ends with "none"</li>
    <li> <b>E{display*=none}</b> css value "display" that contains the substring "none"</li>
    <li> <b>E{display%=2}</b> css value "display" that is evenly divisible by 2</li>
    <li> <b>E{display!=none}</b> css value "display" that does not equal "none"</li>
</ul>
@singleton