> Does anyone know what _NET_FRAME_EXTENTS is supposed to mean?
It is used to notify the client about the width(s) of the
window decoration added by the window manager.
https://standards.freedesktop.org/wm-spec/wm-spec-latest.html
A Client whose window has not yet been mapped can request
of the Window Manager an estimate of the frame extents it
will be given upon mapping. To retrieve such an estimate,
the Client MUST send a _NET_REQUEST_FRAME_EXTENTS message
to the root window. The Window Manager MUST respond by
estimating the prospective frame extents and setting the
window's _NET_FRAME_EXTENTS property accordingly. The Client
MUST handle the resulting _NET_FRAME_EXTENTS PropertyNotify
event. So that the Window Manager has a good basis for
estimation, the Client MUST set any window properties it
intends to set before sending this message. The Client MUST
be able to cope with imperfect estimates.
Rationale: A client cannot calculate the dimensions of
its window's frame before the window is mapped, but some
toolkits need this information. Asking the window manager
for an estimate of the extents is a workable solution. The
estimate may depend on the current theme, font sizes or
other window properties. The client can track changes to
the frame's dimensions by listening for _NET_FRAME_EXTENTS
PropertyNotify events.
