About <DEL> character and Control character.

About <DEL> character and Control character.

[waterloo]

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I am reading Emacs Lisp Reference and can not understand the following
paragraph:

For historical reasons, Emacs treats the <DEL> character as the
control equivalent of `?':

     ?\^? => 127     ?\C-? => 127

As a result, it is currently not possible to represent the character
`Control-?', which is a meaningful input character under X, using
`\C-'.  It is not easy to change this, as various Lisp files refer to
<DEL> in this way.

What I understand is :
?\^? = <DEL>
now we can not represent `Control-?' with `?\ " syntax.

Is it right?

What does "which is a meaningful input character under X, using
`\C-'. " mean ?

Thanks

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Re: About <DEL> character and Control character.

[Barry Margolin]

In article <mailman.3926.1249463831.2239.help-gnu-emacs@gnu.org>,
 waterloo <waterloo2005@gmail.com> wrote:

> I am reading Emacs Lisp Reference and can not understand the following
> paragraph:
> 
> For historical reasons, Emacs treats the <DEL> character as the
> control equivalent of `?':
> 
>      ?\^? => 127     ?\C-? => 127
> 
> As a result, it is currently not possible to represent the character
> `Control-?', which is a meaningful input character under X, using
> `\C-'.  It is not easy to change this, as various Lisp files refer to
> <DEL> in this way.
> 
> What I understand is :
> ?\^? = <DEL>
> now we can not represent `Control-?' with `?\ " syntax.
> 
> Is it right?
> 
> What does "which is a meaningful input character under X, using
> `\C-'. " mean ?

There is no Control-? character in traditional ASCII, which is why it 
was originally OK to use ^? as the way to represent DEL.  But modern 
windowing systems, like X, Windows, and MacOS, allow the control 
modifier to be applied to any character on the keyboard.  This created 
the ambiguity, because now there's a real Control-?.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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