AltGr finger twisters documented?

[Juanma Barranquero]

After an exchange of comments on the Emacs wiki, that left me wondering...

Is there any place in the Emacs documentation that explains that you
*can* type C-M-@, C-@, C-M-\, C-\ and C-] on an AltGr-challenged
keyboard, *provided* that you use the right order, i.e., AltGr, right
Ctrl, and then the modified key?

For example, on my Spanish keyboard:

   C-M-@ => AltGr RCtrl Alt 2
   C-@   => AltGr RCtrl 2
   C-M-\ => AltGr RCtrl Alt º
   C-\   => AltGr RCtrl º
   C-]   => AltGr RCtrl +

It is non-obvious: it doesn't work if you press other key before
AltGr, or if you use left control.

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                    /L/e/k/t/u