(PHP 7)
SessionUpdateTimestampHandlerInterface::validateId — Validate ID
$key
   ) : boolValidates a given session ID. A session ID is valid, if a session with that ID already exists. This function is automatically executed when a session is to be started, a session ID is supplied and session.use_strict_mode is enabled.
keyThe session ID.
   Returns TRUE for valid ID, FALSE otherwise.
   Note that this value is returned internally to PHP for processing.