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

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







http://expect.nist.gov/FAQ.html#q53
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)]
"
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[Category Expect]