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Date: Thu, 4 May 89 23:23:04 EDT
From: ncramer@BBN.COM (Nichael Cramer)
Why is Shift-A not the same as Uppercase A and/or why does having control
bits reverse the sense of what is Uppercase/capital?
There is no meaningful concept of alphabetic case in control characters.
In other words, in "Control-A" or "Meta"-A, the word "A" represents
pressing a particular key; it does not represent a printed glyph that
might look like 1A0 or like 1a0. Since the shift key isn't being used to
select alphabetic case in connection with control characters, we take
advantage of it to expand the space of single-character commands. Thus
Shift is a fifth modifier, like Control, Meta, Hyper, and Super, for
control letters and for mouse clicks.
The rest of your questions relate to internal implementation details
and the "clever" encoding of the shift bit in the representation
of control characters. That's just implementation and shouldn't
be of any concern to you. Common Lisp doesn't define any particular
values to be returned by the CHAR-CODE function.