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Re: Accented variables, and cancelling fractions

From: David Carlisle <davidc@nag.co.uk>
Date: Mon, 4 Aug 2003 12:13:55 +0100
Message-Id: <200308041113.MAA02357@penguin.nag.co.uk>
To: jpederse@wiley.com
CC: www-math@w3.org

  

   Is the set of combining diacritical marks (Unicode blocks U+0300-036F and
   U+20D0-20FF) more appropriate for use as accents (even though most don't
   have symbolic names)? There they do have, for example, an under dot
   (U+0323) in addition to the over dot. In MathML I suppose it would still
   need the <munder> treatment though (outside of <mtext>).


Using combining characters with markup is problematic and explictly
deprecated in the W3C's character model document. If you start an entity
definition with a combining character than a text base unicode
normaliser will attempt to combine the character with the markup rather
than with the intended character. (and will actually succeed in the case
of a combining / and a >, which would make the file non-well formed.
So for MathML we've tried as far as possible to avoid combining
characters,
see:
http://www.w3.org/2003/entities/iso9573-2003doc/9573sec6.html#sec6.2


As Simon commented the spacing diacritics don't quite "feel" right
either, but then Unicode is primarily a plain text convention and
doesn't always work naturally when combined with markup conventions.
MathML renderers only really need a "hook" to tell them which accent is
to be used, especially in "stretchy" accents that expand to cover the
base expression, the accent doesn't really correspond to any unicode
character at all, the character is just being used as a "label".
So I think the non-combining, spacing versions are the best compromise.

   I have a related question: what is the correct way in MathML to tag
   "crossed out" parts of fractions, used to indicate terms that have been
   cancelled? If it is a single letter or number, then the combining solidus
   U+0338 would do the trick, but is there a way to indicate a line through a
   whole expression? Should I use
   <mrow>...the expression...</mrow><mo>&#x0336;</mo> ?

   Thank you.

   John Pedersen
   Content Systems,
   John Wiley & Sons, Inc.


Hmm, I'm not sure. You could use some negative spacing to overlay a /
but it might be hard to get that looking just right. But I've been away
for a few days, perhaps something will occur to me later, or someone
else may have a better suggestion!

David

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Received on Monday, 4 August 2003 07:14:36 GMT

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