On Wed, Apr 19, 2017 at 09:26:23AM +0200, martin rudalics wrote:
> If at this time I do within the just started Emacs
> 
> (set-frame-parameter nil 'undecorated t)
> 
> I get
> 
> /home/martin/emacs-git/trunk/obj-ns/src/emacs: Uncaught exception NSInvalidArgumentException, reason: -[EmacsFSWindow setStyleMask:]: unrecognized selector sent to instance 0x30a37d0

It turns out that GNUStep doesn’t let you change the decorated state
of an existing window. It should be able to create a new undecorated
window.

> Setting the 'parent-frame' parameter of a frame has no impact, neither
> when I do it during frame creation not when doing it at any later time.

I believe it is setting the parent/child relationship, but in GNUStep
it doesn’t seem to mean the child moves with the parent. I think this
is a bug in GNUStep, but the behaviour isn’t documented yet, so I’m
not sure if it’s intentional.

The child will minimise and close with the parent and moving it to (0
0) will put it in the top left corner of the parent.

Except it doesn’t quite, because there’s a hard‐coded titlebar height
for GNUStep which is guaranteed to be wrong for every WM. At least I
think that’s what going on.

Z‐groups are working, but again in GNUStep it seems a bit hit and miss
as the frames seem to forget their state if you click on their
titlebars.
-- 
Alan Third