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

> Date: Fri, 4 Jan 2013 15:35:30 -0800 (PST)
> From: John Brown <[email protected]>
> 
> In any case, I do not really want to interfere with Windows.
> I would rather enable the C-Return binding.

Then you will have to bind it as any other key, because by default
C-Return is unbound.  I don't know why you expected it to be bound.
Bind it to the command completion-at-point.  (You can also invoke that
command by typing ESC TAB -- 2 characters.)