test for CSS attribute selector support

function testAttributeSupport() {
	var head = document.getElementsByTagName('head')[0];
	var style = document.createElement('style');
	var s = 'div[id] {}';
	style.type = 'text/css';

	if (style.styleSheet)
		style.styleSheet.cssText = s;
	else
		style.appendChild( document.createTextNode(s) );

	head.appendChild( style );
	s = style.sheet || style.styleSheet;
	s = (s.rules || s.cssRules)[0];
	return (s.selectorText || s.cssText).toLowerCase() == 'div[id]';
}