- if ( substr( $url, 0, 2 ) === '//' || parse_url( $url, PHP_URL_SCHEME ) ) {
+ // Also skips the rare `behavior` property specifying application's default behavior
+ if (
+ substr( $url, 0, 2 ) === '//' ||
+ parse_url( $url, PHP_URL_SCHEME ) ||
+ substr( $url, 0, 9 ) === '#default#'
+ ) {