This protocol is limited to Xwayland only and is not visible/usable by
any other client.
Mutter uses the following mechanisms to determine if an X11 client
should be granted a grab:
- is "xwayland-allow-grabs" set?
- if set, is the client blacklisted?
- otherwise, has the client set the X11 window property
_XWAYLAND_MAY_GRAB_KEYBOARD on the window using a client message?
- if not, is it a client white-listed either via the default system
list or the settings "xwayland-grab-access-rules"?
https://bugzilla.gnome.org/show_bug.cgi?id=783342
