DBus flags of exposed methods/properties/signals

[Germano Massullo]

Hello. I am practicing with DBus, by using GDBus API. To achieve that
I studied NetworkManager GDBus examples [1].
I have a question. By reading methods/properties/signals exposed by
systemd-logind on DBus [2], I have read things like
readonly t IdleSinceHint = 0;

What does 't' stand for? There are also many other "flags", like 'b', 'as', etc.

Best regards

[1]: https://cgit.freedesktop.org/NetworkManager/NetworkManager/tree/examples/C/glib
[2]: https://freedesktop.org/wiki/Software/systemd/logind/