bug#33553: Document negatively listing fonts for character range

[Eli Zaretskii]

> From: 積丹尼 Dan Jacobson
>       <jidanni@jidanni.org>
> Date: Fri, 30 Nov 2018 06:50:12 +0800
> 
> (info "(emacs) Modifying Fontsets")
> shows how to
> 
> + Use a certain font for a certain range of characters
> 
> + Prohibit a certain font for all characters
> 
> But it doesn't show how to
> 
> + Prohibit a certain font for a certain range of characters

That's because there is no way.  You must instead use another font for
that range of characters.

> So to prohibit a certain font for just one character, the user must
> prohibit it for all characters.

No.

> Or he must hardwire some other arbitrary font to be used for that one
> character, he can not just say don't use a certain font for that
> character.

Yes.  Why is that a problem?

I'm not sure I understand what exactly is the bug you would like to be
fixed here?  There's no documentation bug, AFAICT, as the
documentation describes the facilities we have.