bug#18059: 24.3.92; defvar and special variables

[Drew Adams]

> > +Note that specifying a value, even @code{nil}, marks the variable as
> > +special permanently.  Whereas if @var{value} is omitted then the
> > +variable is only marked special locally (i.e. within the current file
> > +or let-block).  This can be useful for suppressing byte compilation
> > +warnings, see @ref{Compiler Errors}.
> 
> After reading this and thinking about it, I'm confused now what the
> extent of `defvar' without a specified value is.
> 
> In the case of a file, does it mean that the variable is considered
> special for the rest of the file, or for the whole file?

Apologies for not following this. Question: is some change
in behavior being discussed here or is it just a question
about improving documentation of the longstanding behavior?