h1. jQuery Selector

h3. Selector tools and reverse mapping for jQuery

* Parse and examine the AST for a selector
* Calculate the specifity of a selector
* Determine if a single element matches a selector ($().is equivilent) much faster that jQuery 

h3. Intro

jQuery has an excellent CSS 3 selector engine built in called Sizzle. However, it's clear focus is on filtering a set of elements down to the set that matches a selector.

jQuery.concrete has a usage pattern quite different from that optimized for by Sizzle. It reuses a small set of selectors (making a more complicated initial parsing step acceptable)
and checks if a single element matches those selectors. In this case, Sizzle can be quite slow.

h3. Usage

Usual usage of jQuery selector:

var sel = $.selector('#foo');
sel.matches(element);

element must be a raw DOM object, not a jQuery element, sequence of elements or anything else

h3. Compatibility

jQuery.selector aims to be 100% compatible with Sizzle (except a couple of corner cases, noted below). Sizzle implements most of the CSS 3 spec plus several extensions. 

One set of extensions Sizzle has is a set of pseudo-classes that filter the currently selected set. These pseudo-classes are ':first', ':last', ':even', ':odd', ':eq', ':nth', ':lt', ':gt'.
These pseudo-classes are not supported in jQuery.selector, as they don't make sense when the working set is always a single element.

jQuery.selector currently passes the jQuery selector unit test suite, with the exception of the psuedo-classes mentioned above