/**
* Prepend a path to relative URIs in CSS files
*
* @param string $css
* @param string $path The path to prepend.
* @param integer $browserCacheId
* @param array $browserCacheExtensions
*
* @return string
*/
private static function _prepend($css, $path, $browserCacheId = 0, $browserCacheExtensions = array())
{
self::$_prependRelativePath = $path;
self::$_browserCacheId = $browserCacheId;
self::$_browserCacheExtensions = $browserCacheExtensions;
$css = self::_trimUrls($css);
// append
$css = preg_replace_callback('/@import\\s+([\'"])(.*?)[\'"]/', array(self::$className, '_processUriCB'), $css);
$css = preg_replace_callback('/url\\(\\s*([^\\)\\s]+)\\s*\\)/', array(self::$className, '_processUriCB'), $css);
return $css;
}