implementing CSS3 specificity algorithm (with some extensions) in JS

code.js

/**
 * calculates a set of specificity scores for a CSS selector
 * based on (but extending) the CSS3 specificity algorithm:
 * http://reference.sitepoint.com/css/specificity
 *
 * @param {string} selector
 */
function specificity(selector) {
	var specificity = [0,0,0,0,0], idx, matches, tmp = 0,
		selectors = selector.split(/\s*,\s*/)
	;

	for (idx in selectors) {
		// id selectors
		matches = selectors[idx].match(/#/g);
		if (matches) specificity[1] += matches.length;
		// class selectors
		matches = selectors[idx].match(/\./g);
		if (matches) specificity[2] += matches.length;
		// attribute selectors
		matches = selectors[idx].match(/\[.+\]/g);
		if (matches) specificity[2] += matches.length;
		// pseudo-element selectors
		matches = selectors[idx].match(/:(?:first-letter|first-line|before|after|:selection)/g);
		if (matches) {
			tmp = matches.length;
			specificity[3] += tmp;
		}
		// pseudo-(element and class) selectors
		matches = selectors[idx].match(/:/g);
		if (matches) specificity[2] += (matches.length - tmp); // filter out the count of lower-precedence matches of pseudo-elements
		tmp = 0;
		// child, adjacent-sibling, and general-sibling combinators (Note: extension to CSS3 algorithm)
		matches = selectors[idx].match(/[+>~]/g);
		if (matches) specificity[4] += matches.length;
		// element type selectors (note: must remove everything else to find this count)
		selectors[idx] = selectors[idx]
		.replace(/\(.*?\)/g,"")
		.replace(/\[.*?\]/g,"")
		.replace(/[.#:][^ +>~]*/ig,"");
		matches = selectors[idx].match(/[^ +>~]+/g);
		if (matches) specificity[3] += matches.length;
	}

	return specificity;
};

use.js

// Note #1: the fifth score in the matrix is for the > ~ and + combinators, one of my extensions to the CSS3 specificity algorithm

// Note #2: I made multiple rules (separated by ,) additive, as I think that also makes for a more specific rule, as opposed to two separate rules). See the first and second examples below.

specificity("div")   // [0, 0, 0, 1, 0]
specificity("div, span")   // [0, 0, 0, 2, 0]
specificity("div#foo")   // [0, 1, 0, 1, 0]
specificity("div#foo .blah")   // [0, 1, 1, 1, 0]
specificity("div#foo > .blah")   // [0, 1, 1, 1, 1]
specificity("div#foo > .blah table")   // [0, 1, 1, 2, 1]
specificity("div#foo > .blah ~ table")   // [0, 1, 1, 2, 2]
specificity("div#foo > .blah ~ table.blah.blah2")   // [0, 1, 3, 2, 2]