diff -u -r1.390 startup.el
--- lisp/startup.el	22 Nov 2005 03:32:50 -0000	1.390
+++ lisp/startup.el	26 Dec 2005 19:48:55 -0000
@@ -149,7 +149,8 @@
     ("--vertical-scroll-bars" 0 x-handle-switch vertical-scroll-bars t)
     ("--line-spacing" 1 x-handle-numeric-switch line-spacing)
     ("--border-color" 1 x-handle-switch border-color)
-    ("--smid" 1 x-handle-smid))
+    ("--smid" 1 x-handle-smid)
+    ("--parent-id" 1 x-handle-parent-id))
   "Alist of X Windows options.
 Each element has the form
   (NAME NUMARGS HANDLER FRAME-PARAM VALUE)
diff -u -r1.184 x-win.el
--- lisp/term/x-win.el	2 Nov 2005 21:43:21 -0000	1.184
+++ lisp/term/x-win.el	26 Dec 2005 19:48:59 -0000
@@ -181,6 +181,15 @@
   (setq initial-frame-alist (cons (cons 'name x-resource-name)
 				  initial-frame-alist)))
 
+;; Handle the --parent-id option.
+(defun x-handle-parent-id (switch)
+  (or (consp x-invocation-args)
+      (error "%s: missing argument to `%s' option" (invocation-name) switch))
+  (setq parent-id (string-to-number (car x-invocation-args))
+	x-invocation-args (cdr x-invocation-args))
+  (setq initial-frame-alist (cons (cons 'parent-id parent-id)
+				  initial-frame-alist)))
+
 (defvar x-display-name nil
   "The X display name specifying server and X frame.")
 
diff -u -r1.380 emacs.c
--- src/emacs.c	23 Nov 2005 07:19:03 -0000	1.380
+++ src/emacs.c	26 Dec 2005 19:49:03 -0000
@@ -322,6 +322,7 @@
 --title, -T TITLE               title for initial Emacs frame\n\
 --vertical-scroll-bars, -vb     enable vertical scroll bars\n\
 --xrm XRESOURCES                set additional X resources\n\
+--parent-id XID                 set parent window\n\
 --help                          display this help and exit\n\
 --version                       output version information and exit\n\
 \n"
@@ -1859,6 +1860,7 @@
   { "-title", 0, 10, 1 },
   { "-name", "--name", 10, 1 },
   { "-xrm", "--xrm", 10, 1 },
+  { "-parent-id", "--parent-id", 10, 1 },
   { "-r", "--reverse-video", 5, 0 },
   { "-rv", 0, 5, 0 },
   { "-reverse", 0, 5, 0 },