Alan Mackenzie wrote:
>> It's what Emacs does now, and it works well enough.  And the basic idea
>> >isn't a new principle: Emacs has done it for decades for many ASCII
>> >characters, e.g., HT.  So it is not a problem in practice.
> It will be a problem in practice.  It will by lying about what character
> in the buffer the glyph on the screen represents.

Again, there's nothing new here: Emacs has been "lying" in that way for decades 
for HT and for several other ASCII characters, and it works in practice.

>   It will be ambiguous:

That's easily enough fixed.  I installed the attached patch, which uses shadow 
glyphs for quote substitutions in ASCII-only displays.  If you prefer underline 
or some other glyph face on your console please feel free to change the code.

>> text-quoting-style doesn't do anything for info files, or
>> for other text files containing curved quotes.
>
> That's an argument for an additional facility for Info

The additional facility I proposed would work for info, and would also work for 
*Help* buffers and diagnostics and would render text-quoting-style unnecessary.