"Escape-A", for example, is
    send \033A

"Control-c", for example, is
    send \003





http://expect.sourceforge.net/FAQ.html#q54,
http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?ASCII+character+table


See also "[How Expect sees function keys]".

[Helmut Giese] mentions that "[[t]]o go from an arbitrary [ASCII] character
(say X) to 
its 'control' code (Ctrl X) just do
    set ctrl [expr ($char & 01xF)]
"

[PYK] 2016-02-13:  To derive the [ASCII] control character from the common
notation for control characters, [Bit Twiddling%|%twiddle] the bits on the
corresponding printing character, e.g. "X":


======
set char X
set ctrl [expr {[scan $char %x] & 0x1F}]
======

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