public static function filterTag(Tag $tag, TagStack $tagStack, array $hosts, array $sites, $cacheDir)
	{
		// Always invalidate this tag
		$tag->invalidate();

		if ($tag->hasAttribute('url'))
		{
			$url    = $tag->getAttribute('url');
			$siteId = self::getSiteIdFromUrl($url, $hosts);
			if (isset($sites[$siteId]))
			{
				$attributes = self::getAttributes($url, $sites[$siteId], $cacheDir);
				if (!empty($attributes))
				{
					self::createTag(strtoupper($siteId), $tagStack, $tag)->setAttributes($attributes);
				}
			}
		}
	}