A subcommand of [Tk]'s [winfo] command.

http://www.purl.org/tcl/home/man/tcl8.5/TkCmd/winfo.htm

'''winfo id''' ''window''

Returns a hexadecimal string giving a low-level platform-specific identifier for ''window''. On Unix platforms, this is the X window identifier. Under Windows, this is the Windows HWND. On the Macintosh the value has no meaning outside Tk.

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''See also:''
   * [wm frame]
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Notice that the return value of [[winfo id ...]] is the id used
by [toplevel] and [wish] in
    toplevel ... -use $id
and
    wish ... -use $id

Here's an example:
    label .t1 -text Above
    label .t2 -text Below
    frame .holder -container 1
    pack .t1 .holder .t2
    exec wish other_application.tcl -use [winfo id .holder] &

[[Include an image here.]]

Incidental remark:  when [CL] substitutes
    exec tclkit tiny.tcl -use [winfo id .holder] &
for that last line, while running on WinNT, with tiny.tcl having content
    pack [.button -text "Push me" -command exit]
everything comes up OK.  When the button is pushed, "Dr. Watson"
appears.  Dismissing it eventually results in a whited-out frame
"hole" in the embedding Wish.  Is this an error in Tclkit 8.4a3?

Is it a bug, that the results of winfo id and xwininfo differ in the window id exactly by one ?

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