function getRootDomain($url)
{
// Get rid of junk
	if(!isValidUrl($url)) { return false; }

// parse the url to get the host name
	$parsedUrl = parse_url($url);

// break it apart by the '.' and flip it around
	$parts = array_reverse(explode('.',$parsedUrl['host']));

// remove all but the last three parts (e.g., 'www.site.com' or
'site.com.tw' or if there's only two 'site.com')
	while(count($parts) > 3)
	{
		array_pop($parts);
	}

// if there are three parts, and the middle part is more than 3
characters, then ditch the first part
// example:  www.site.com - 'site' > 3 so ditch the 'www', site.com.tw
= 'com' isn't > 3, so keep the 'site'
	if( isset($parts[2]) && strlen($parts[1]) > 3) { unset($parts[2]); }

// pass back the reassembled root domain name
	return implode('.',array_reverse($parts));
}