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RE: Mirroring Unicode symbols in Arabian

From: Paul Topping <pault@dessci.com>
Date: Wed, 20 Feb 2013 22:24:53 +0000
To: Murray Sargent <murrays@exchange.microsoft.com>, Tom Leathrum <leathrum@jsu.edu>
CC: Neil Soiffer <neils@dessci.com>, Kent Karlsson <kent.karlsson14@telia.com>, David Carlisle <davidc@nag.co.uk>, "Daniel Marques" <dani@wiris.com>, "www-math@w3.org" <www-math@w3.org>, Khaled Hosny <khaledhosny@eglug.org>
Message-ID: <B6C5B1ABA88AF446821B281774E6DB710D75FE@FERMAT.corp.dessci>
Murray,

Based on your earlier "semantics" vs "display" argument, if the mirror of an existing Unicode character has unique semantics, then it should also have its own, separate Unicode point. However, a font maker that recognizes this is forced to assign a PUA point to the mirrored character unless they want to delay the release of their font until after the new character has been added to Unicode. (I'm assuming there's no combining character whose display interpretation is to mirror the character to which it is applied, right?) While CSS may have mechanisms to "style" a character to display its mirrored version, that would not be the proper way to deal with a character with different semantics. Search and other text-based processes would and should ignore the CSS applied to text. At least that is my understanding.

As a maker of math editing software, I dislike having to deal with fonts' use of PUA to map characters that have no Unicode point. These PUA point assignments are usually only meaningful in the context of a single font which makes them hard to deal with. However, each of those PUA characters is a potential new Unicode point. Given that Unicode has to evolve, I would assume that the UC expects to occasionally add new points based on a characters use in the real world. In the modern world, these PUA characters constitute such use.

Paul

> -----Original Message-----
> From: Murray Sargent [mailto:murrays@exchange.microsoft.com]
> Sent: Wednesday, February 20, 2013 2:07 PM
> To: Paul Topping; Tom Leathrum
> Cc: Neil Soiffer; Kent Karlsson; David Carlisle; Daniel Marques; www-
> math@w3.org; Khaled Hosny
> Subject: RE: Mirroring Unicode symbols in Arabian
> 
> I really do not like the idea of using PUA code points for mirrored
> glyphs except perhaps as a private hack. PUA codepoints are nonstandard
> by definition and should be limited to experimental usage. (I've been a
> member of the Unicode Technical Committee since 1994, so perhaps I'm a
> bit brainwashed :-)) Meanwhile the OpenType approach is a standard,
> widely used way of doing such things.
> 
> Murray
> 
> -----Original Message-----
> From: Paul Topping [mailto:pault@dessci.com]
> Sent: Wednesday, February 20, 2013 1:13 PM
> To: Tom Leathrum
> Cc: Neil Soiffer; Kent Karlsson; David Carlisle; Daniel Marques; www-
> math@w3.org; Murray Sargent; Khaled Hosny
> Subject: RE: Mirroring Unicode symbols in Arabian
> 
> Right. I just wanted to point out to the math buffs on the thread that
> if the only mechanism to show reversed glyphs is via RTL or some app-
> specific access to OpenType features. I am not sure if CSS gives the
> necessary control to show these glyphs in HTML content. If anyone wants
> these reversed glyphs to be used in math, then font vendors should be
> encouraged to give them PUA points in their fonts and, presumably,
> there would be a case to be made to propose non-PUA points for them in
> Unicode. My point may be off-topic.
> 
> Paul
> 
> > -----Original Message-----
> > From: Tom Leathrum [mailto:leathrum@jsu.edu]
> > Sent: Wednesday, February 20, 2013 12:10 PM
> > To: Paul Topping
> > Cc: Neil Soiffer; Kent Karlsson; David Carlisle; Daniel Marques; www-
> > math@w3.org; Murray Sargent; Khaled Hosny
> > Subject: Re: Mirroring Unicode symbols in Arabian
> >
> > If I may interject here:
> >
> > Paul, I think Murray's point about semantics addresses your concern,
> > because if there is a semantic difference between reversed symbols in
> > LTR then they will be represented in different Unicode values.
> > Consider for example U+2282 "subset" and U+2283 "superset" -- the
> > glyphs are mirror-images, and both are marked as mirror="Y" for RTL.
> > RTL would have the visual effect of swapping these two glyphs, but in
> > fact their Unicode values wouldn't change because the semantics would
> > still be the same -- U+2282 would be semantically "subset" whether it
> > is mirrored or not, and in RTL the glyph for it would look (to LTR
> > readers) like a superset symbol.  Clear as mud?
> >
> >
> > ----- Original Message -----
> > From: "Paul Topping" <pault@dessci.com>
> > To: "Murray Sargent" <murrays@exchange.microsoft.com>, "Khaled Hosny"
> > <khaledhosny@eglug.org>
> > Cc: "Neil Soiffer" <neils@dessci.com>, "Kent Karlsson"
> > <kent.karlsson14@telia.com>, "David Carlisle" <davidc@nag.co.uk>,
> > "Daniel Marques" <dani@wiris.com>, www-math@w3.org
> > Sent: Wednesday, February 20, 2013 1:46:15 PM
> > Subject: RE: Mirroring Unicode symbols in Arabian
> >
> > So this means that reversing a symbol to express a mathematical
> > concept is unavailable to non-RTL text even though the fonts and the
> > font rendering mechanism has the capability.
> >
> > Paul
> >
> > > -----Original Message-----
> > > From: Murray Sargent [mailto:murrays@exchange.microsoft.com]
> > > Sent: Wednesday, February 20, 2013 11:36 AM
> > > To: Paul Topping; Khaled Hosny
> > > Cc: Neil Soiffer; Kent Karlsson; David Carlisle; Daniel Marques;
> > > www- math@w3.org
> > > Subject: RE: Mirroring Unicode symbols in Arabian
> > >
> > > I meant that the codes for the mirrored integral, etc., are exactly
> > the
> > > same as the unmirrored symbols. The display software just mirrors
> > them
> > > in RTL math zones. If you use OpenType, you used the 'rtlm' feature
> > or
> > > shaping, as the characters warrant. This is the same thing as for
> > > mirrored characters that have mirrored character counterparts. An
> > open
> > > paren is U+0028 whether it's mirrored or not.
> > >
> > > Murray
> > >
> > > -----Original Message-----
> > > From: Paul Topping [mailto:pault@dessci.com]
> > > Sent: Wednesday, February 20, 2013 11:31 AM
> > > To: Murray Sargent; Khaled Hosny
> > > Cc: Neil Soiffer; Kent Karlsson; David Carlisle; Daniel Marques;
> > > www- math@w3.org
> > > Subject: RE: Mirroring Unicode symbols in Arabian
> > >
> > > Not sure how this answers my question.
> > >
> > > Paul
> > >
> > > > -----Original Message-----
> > > > From: Murray Sargent [mailto:murrays@exchange.microsoft.com]
> > > > Sent: Wednesday, February 20, 2013 11:24 AM
> > > > To: Paul Topping; Khaled Hosny
> > > > Cc: Neil Soiffer; Kent Karlsson; David Carlisle; Daniel Marques;
> > www-
> > > > math@w3.org
> > > > Subject: RE: Mirroring Unicode symbols in Arabian
> > > >
> > > > Mirrored glyphs are a display feature, not a semantic one.
> > > >
> > > > Murray
> > > >
> > > > Paul Topping asked, "If access to these characters requires use
> of
> > > > this OpenType feature, does it imply that such characters will
> not
> > be
> > > > accessible from applications that simply process Unicode text
> > strings
> > > > (eg, web browsers and most other apps)?"

Received on Wednesday, 20 February 2013 22:25:23 GMT

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