allow vimeo and youtube iframes in HTMLPurifier

sanitize.php

  /**
	 * Sanitize string input
	 * @param string $dirty_html
	 * @return string
	 */
	public static function purify( $dirty_html )
	{
		$config = HTMLPurifier_Config::createDefault();
		$config->set('HTML.SafeIframe', true);
		$config->set('URI.SafeIframeRegexp', '%^(https?:)?//(www\.youtube(?:-nocookie)?\.com/embed/|player\.vimeo\.com/video/)%'); //allow YouTube and Vimeo
		$purifier = new HTMLPurifier($config);
		$clean_html = $purifier->purify($dirty_html);

		return $clean_html;
	}