/** * Retrieve registered license option keys via `apppresser_license_keys_to_check` filter * @since 1.0.1 * @return array All license option keys */ public static function license_keys() { if (empty(self::$license_keys)) { $appp_settings = self::run(); self::$license_keys = apply_filters('apppresser_license_keys_to_check', self::$license_keys, $appp_settings); } return self::$license_keys; }