I did just find two references to 'fullscreen used as an alias to
'fullboth, but it's not documented and not implemented in all front ends
so its use is not portable.  I suggest we remove these or we document it
and correct all the front ends.  It looks like copy pasta, rather than by
intent.

pgtkfns.c:

static Lisp_Object
frame_geometry (Lisp_Object frame, Lisp_Object attribute)
{
  struct frame *f = decode_live_frame (frame);
  Lisp_Object fullscreen_symbol = Fframe_parameter (frame, Qfullscreen);
  bool fullscreen = (EQ (fullscreen_symbol, Qfullboth)
    || EQ (fullscreen_symbol, Qfullscreen));

nsfns.m:

static Lisp_Object
frame_geometry (Lisp_Object frame, Lisp_Object attribute)
{
  struct frame *f = decode_live_frame (frame);
  Lisp_Object fullscreen_symbol = Fframe_parameter (frame, Qfullscreen);
  bool fullscreen = (EQ (fullscreen_symbol, Qfullboth)
    || EQ (fullscreen_symbol, Qfullscreen));

On Tue, Feb 18, 2025 at 12:50 PM Ship Mints <shipmints@gmail.com> wrote:

> In frame.el's toggle-frame-fullscreen and toggle-frame-maximized, these
> look like either typos, or vestigial references.  The frame-parameter
> fullscreen is never set to 'fullscreen nor is the value 'fullscreen used in
> other places in Emacs.  It is an undocumented value, appearing nowhere.
> Unless I missed something.
>
> I reviewed below sources and relevant headers:
>
> android.c
> androidfns.c
> androidterm.c
> emacs.c
> frame.c
> gtkutil.c
> haikufns.c
> haikuterm.c
> pgtkfns.c
> pgtkterm.c
> term.c
> w32fns.c
> w32term.c
> xfns.c
> xmenu.c
> xterm.c
> nsfns.m
> nsterm.m
>
> -Stephane
>