private function html_attr($matches){
		
		// could be empty?
		$url = trim($matches[2]);
		
		$schemes = array('data:', 'magnet:', 'about:', 'javascript:', 'mailto:', 'tel:', 'ios-app:', 'android-app:');
		if(starts_with($url, $schemes)){
			return $matches[0];
		}
		
		return str_replace($url, proxify_url($url, $this->base_url), $matches[0]);
	}