How and what benefit can I take by including Sizzle.js along with jquery1.4.2?

Question

latest jquery 1.4.2 downloaded from jquery.com comes with Sizzle.js also.

How and what benefit can I take from included Sizzle.js?

Is Sizzle.js a standalone library?

Why it's included inside jquery library, for what purpose?

/*!
 * jQuery JavaScript Library v1.4.2
 * http://jquery.com/
 *
 * Copyright 2010, John Resig
 * Dual licensed under the MIT or GPL Version 2 licenses.
 * http://jquery.org/license
 *
 * Includes Sizzle.js
 * http://sizzlejs.com/
 * Copyright 2010, The Dojo Foundation
 * Released under the MIT, BSD, and GPL Licenses.
 *
 * Date: Sat Feb 13 22:33:48 2010 -0500
 */

while this is mentioned on sizzle.js website

Completely standalone (no library dependencies)

Answer 1

Sizzle.js is a JavaScript library that implements a "CSS selector engine designed to be easily dropped in to a host library." jQuery uses it internally for its CSS selection needs. If you wanted a CSS engine and had no need for all the other JavaScript benefits of jQuery, you could use Sizzle.js separately.