[racket] Simple keybinding question

I want to set up some user defined keybindings to type unicode letters with
diacritical marks into DrRacket but I want to use the same keybinding
system I'm used to.  I'm able to set up the user defined keybindings that
use only one control character.  But I can't figure out how to set up
keybindings that use two control characters pressed simultaneously.  For
example I can't figure out how to set a keybinding up so that Ctrl,Alt and
r pressed simultaneously will print r with dot underneath and macron on
top, i.e. "ṝ"

I'm using Racket on Windows.

I tried the following in my user defined keybindings file..

#lang s-exp framework/keybinding-lang
(keybinding "c:a" (λ (editor evt) (send editor insert "ā")))
(keybinding "c:i" (λ (editor evt) (send editor insert "ī")))
(keybinding "c:u" (λ (editor evt) (send editor insert "ū")))
(keybinding "m:t" (λ (editor evt) (send editor insert "ṭ")))
.
.
.
(keybinding "c:m:r" (λ (editor evt) (send editor insert "ṝ")))

Everything works except the last keybinding which I thought would mean
ctrl,alt, and r pressed simultaneously.

Thanks in advance
Harry Spier
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