public function allowMimetype($Mimetype) {
        if ( ! $this->returnUrl() ) return false;
        if ( isset($this->claim->accept_media_types) ) {
            $ma = $Mimetype;
            if ( ! is_array($ma) ) $ma = array($Mimetype);
            $m = new Mimeparse;
            $allowed = $m->best_match($ma, $this->claim->accept_media_types);
            if ( $Mimetype != $allowed ) return false;
            return true;
        }
        return false;
    }