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RE: C-u C-space


From: Drew Adams
Subject: RE: C-u C-space
Date: Wed, 9 May 2007 15:54:37 -0700

> Now I am trying to find out what command is associated with C-u 
> C-space. I do C-h k C-u .
> 
> It appears <<C-u runs the command universal-argument>> . I did 
> not arrive to press C-space.
> 
> Is it a bug? Or I used wrong describe-key ?

It is not a bug. It is the way Emacs works. You need to read the Emacs manual 
section on C-u (prefix argument). 

Once you understand that, you'll understand that you need only do C-h C-SPC. 
That will give you an explanation of the command bound to C-SPC, 
`set-mark-command', and that explanation will tell you what `C-u' means in that 
context:

 C-SPC runs the command set-mark-command
 ...

 With argument, e.g. C-u C-@, jump to mark, and pop a
 new position for mark off the local mark ring...

 With a double C-u prefix argument, e.g. C-u C-u C-@,
 unconditionally set mark where point is.

IOW, C-u has different meanings and behaviors, depending on what key sequence 
follows it. Use C-h on the base key sequence to find out about its behavior 
when it is modified by C-u.





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