fa is the dedicated namespace for the freearchive project.
You have two main action available and understood by the bot.
fa:archive without any value specify the action to get the machine tagged URI and archive it. This action is often used for mirroring a single document located at the specified URI.
fa:mirror is mirroring the tagged URI and archiving the file containing the mirrored URI.
The level of recursion is 2 by default.
fa:mirror="2" specify the level of recursion to 2.