Re: [SOLVED] <C-return> is undefined in nXML mode

> Apparently that line does not stand alone. My .emacs looks
> like this (just one line):
> (define-key map [C-return] 'completion-at-point)
> 
> When I load emacs, I get:
> Symbol's value as variable is void: map
> 
> I would probably have to copy the entire
> (defvar nxml-mode-map ... map) expression.

No - see below.

> Assuming that it worked, if my .emacs is loaded just
> once at startup, wouldn't my key binding be overwritten each time
> nXML mode is loaded?

No - if a variable (e.g. `nxml-mode-map') already has a value then the defvar
becomes a no-op when loaded.  This means that you can use, say, `setq' to give a
variable a value in your .emacs and not have that value overridden by later
loading some library that defvars the same variable.

> No doubt there is a way around that, but that
> is too much digging around in the manual for me right now.

If the keymap variable in question is bound (defined) from the outset, from
emacs -Q, then you can put just this in your .emacs:

(define-key nxml-mode-map [C-return] 'completion-at-point)

More likely, however, the keymap is not bound at the outset, but only when its
library is loaded (IOW, the library is not preloaded).

In this case, `nxml-mode-map' is not bound until library nxml-mode.el is loaded.
So you need to tell Emacs to define the key after loading the library that
defines the keymap.  Here is one way to do that:

(eval-after-load "nxml-mode"
  '(define-key nxml-mode-map [C-return] 'completion-at-point))

However, when it comes to major modes, which is the case here, you need only put
the key definition on the mode hook.  This is recommended - better than using
`eval-after-load'.

(add-hook 'nxml-mode-hook
          (lambda ()
            (define-key nxml-mode-map
              [C-return] 'completion-at-point)))

See (emacs) `Hooks' and http://www.emacswiki.org/emacs/ModeHooks.

But see this first: (emacs) `Init Rebinding'.  It discusses exactly the question
you raise.

The Emacs manual is your friend: `C-h r', then `i' to find indexed topics or
`C-s' to search the full text.

If you read about a few basics such as these (binding keys, using libraries and
major modes) then you will help yourself a lot when it comes to other questions
that come up.