treewide: add literalDocBook text to options with complex defaults

some options have default that are best described in prose, such as
defaults that depend on the system stateVersion, defaults that are
derivations specific to the surrounding context, or those where the
expression is much longer and harder to understand than a simple text
snippet.

1 files changed, 3 insertions, 0 deletions

diff --git a/nixos/modules/services/x11/display-managers/default.nix b/nixos/modules/services/x11/display-managers/default.nix
index 3adb50c678e..58e4fe04f37 100644
--- a/nixos/modules/services/x11/display-managers/default.nix
+++ b/nixos/modules/services/x11/display-managers/default.nix
@@ -279,6 +279,9 @@ in
             defaultSessionFromLegacyOptions
           else
             null;
+        defaultText = literalDocBook ''
+          Taken from display manager settings or window manager settings, if either is set.
+        '';
         example = "gnome";
         description = ''
           Graphical session to pre-select in the session chooser (only effective for GDM, LightDM and SDDM).