Index: src/wp-admin/customize.php
===================================================================
--- src/wp-admin/customize.php	(revision 25830)
+++ src/wp-admin/customize.php	(working copy)
@@ -172,6 +172,13 @@
 	if ( is_ssl() && ! $cross_domain )
 		$allowed_urls[] = home_url( '/', 'https' );
 
+	/**
+	 * Filter the allowed URLS.
+	 *
+	 * @since 3.4.0
+	 *
+	 * @param array $allowed_urls An array of allowed URLs.
+	 */
 	$allowed_urls = array_unique( apply_filters( 'customize_allowed_urls', $allowed_urls ) );
 
 	$fallback_url = add_query_arg( array(