What does this Release Modifier do?

Question

I am currently programming a Window Manager for X11 using python-xlib. So far, I used myself the Simplewm by Sqizit as an orientation, which is orientated at PLWM.

And in both WMs, you can find a Release Modifier, which is defined as

RELEASE_MODIFIER = Xlib.X.AnyModifier << 1

But in both, there is no further explanation about what exactly this modifier does. I haven't found anything on Google either.

So, if any Xlib-Expert could explain to me what this thing is (I think it should be understandable for C Programmers as well), I'd be very grateful :)

Answer 1

The only reference I could find is in the Sawfish WM programming manual, which says

There are two special modifiers: the Any prefix matches any set of modifiers; the Release modifier matches key-release events instead of the default key-presses.