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Re: display table for eight-bit-graphic

From: Dave Love
Subject: Re: display table for eight-bit-graphic
Date: 03 Feb 2003 14:32:44 +0000
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2

Kenichi Handa <address@hidden> writes:

> What I object is to setting up the display table as now by default.


[The original of these never reached me:]

> address@hidden (Kai Gro├čjohann) writes:
> > "Ehud Karni" <address@hidden> writes:
> >>  I agree. For persons in the ISO-8859-x languages, the 8 bit graphics
> >>  is much better than the octal representation.

Displaying them as graphics is actually worse for people in locales
where the graphics might make sense, but are actually misleading.  Do
you really want undecodeable utf-8 byte sequences, or GBK &c, to
display as Hebrew characters?

> > It might seem so at first sight, but there are problems later on: for
> > instance, you can't search for the 8bit graphics characters by typing
> > Latin-1 characters, and people will surely be *very* surprised that
> > they can't find their characters!

The point is that these aren't actually well-defined characters --
they're random bytes.  If you were sure they represented, say, Latin-1
code points, you could treat them similarly to equivalent characters
from other charsets using translation-table-for-input, but then you
should have decoded the text correctly.

> I agree with that.  Showing different characters by the same
> glyph is the source of confusion at least for novice users.

That sort of thing is also a possible security-type risk.  There are
potential exploits from conning people into thinking the text is
different from what it actually is.

> > Maybe it would be useful to highlight the graphics characters in some
> > way so that it is clear that they aren't normal characters.
> I'm not sure that is a good idea.  Highlighting means many
> things.  Octal displaying is far better to indicate that
> they aren't normal characters.

Exactly.  The only reasonable alternative would be to display them
with single-width glyphs or suitably-propertized text that displayed
the binary values somehow.  I think Yudit does that, but I wouldn't
suggest following it, especially as the glyph contents would typically
be too small.

[It is, in principle, a good idea to flag possibly confusing
characters with faces, such as latin1-disp now allows.  That doesn't
actually work well in practice, since the face information allowed in
the display table doesn't get merged by redisplay.  Thus if you
underline substitutions, they don't inherit the foreground/background
of the adjacent text.  I don't know whether or not this is actually a

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