[gtk+] Document GDK_DISPLAY_XDISPLAY

[Matthias Clasen <matthiasc src gnome org>]

commit 53522f3c258c5735b531a0121c30262dce7fdb9c
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Dec 26 12:53:20 2017 -0500

    Document GDK_DISPLAY_XDISPLAY

 gdk/x11/gdkx11display.h |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/gdk/x11/gdkx11display.h b/gdk/x11/gdkx11display.h
index c432af9..d820519 100644
--- a/gdk/x11/gdkx11display.h
+++ b/gdk/x11/gdkx11display.h
@@ -67,6 +67,14 @@ GDK_AVAILABLE_IN_3_94
 Cursor        gdk_x11_display_get_xcursor      (GdkDisplay  *display,
                                                 GdkCursor   *cursor);
 
+/**
+ * GDK_DISPLAY_XDISPLAY:
+ * @display: a #GdkDisplay
+ *
+ * Returns the display of a #GdkDisplay.
+ *
+ * Returns: an Xlib Display*
+ */
 #define GDK_DISPLAY_XDISPLAY(display) (gdk_x11_display_get_xdisplay (display))
 
 GDK_AVAILABLE_IN_ALL