bug#33179: 26; Doc string of `filter-buffer-substring'

[Drew Adams]

> > For what it's worth, I read it like Drew does.  I also think giving
> > "characters" as an example doesn't make much sense, because I can't
> > really think of characters so "special to a buffer" that they "should
> > not be copied into other buffers".  Grepping the Emacs source, the
> only
> > example usage I found was in org-indent.el, which uses it to exclude
> > text properties, so I propose changing the docstring example
> > accordingly.
> >
> This patch is fine with me, thanks.

Thanks, guys.