Variable: window-system-version
window-system-version is a variable defined in dispnew.c.
This variable is obsolete since 24.3; it does not give useful information.
Value
nil
Documentation
The version number of the window system in use.
For X windows, this is 11.
Probably introduced at or before Emacs version 18.52.
Source Code
// Defined in /usr/src/emacs/src/dispnew.c
DEFVAR_LISP ("window-system-version", Vwindow_system_version,
doc: /* The version number of the window system in use.
For X windows, this is 11. */);