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Re: [MathML3-last-call] mathvariant

From: Karl Tomlinson <w3@karlt.net>
Date: Wed, 14 Oct 2009 09:40:24 +1300
CC: Sam Dooley <sam@integretechpub.com>
To: www-math@w3.org
Message-ID: <87k4yz9gef.fsf@karlt.net>
Thank you for looking at this.

Sam Dooley writes:

> <p>In principle, any <att>mathvariant</att> value may be used with any
> character data to define a specific symbolic token.  In practice,
> only certain combinations of character data and <att>mathvariant</att>
> values will be visually distinguished by a given renderer.  For example,
> there is no clear-cut rendering for a "fraktur alpha" or a "bold italic
> Kanji" character, and the <att>mathvariant</att> values "initial",
> "tailed", "looped", and "stretched" are appropriate only for Arabic
> characters.</p>
> [...]
> Note that the appearance
> of a mathematical alphanumeric symbol character should not be altered
> by surrounding <att>mathvariant</att> or other style declarations.</p>
> <p>Renderers should support those combinations of character data and
> <att>mathvariant</att> values that correspond to Unicode characters,
> and that they can visually distinguish using available font
> characters.

This sentence says "should" ...

> Renderers may ignore or support those combinations of character data
> and <att>mathvariant</att> values that do not correspond to an assigned
> Unicode code point,

... and this sentence says "may", implying that the better
behavior for renderers is to alter the appearance of all
non-mathematical-alphanumeric-symbol characters according to the
mathvariant attribute when possible.

This would be a change from MathML2, so I just want to check that
this has been thought through.

This would effectively mean that almost all
non-mathematical-alphanumeric-symbol characters in an mi element
without an explicit mathvariant attribute should be rendered in an
italic form.

One example to consider is U+221E INFINITY.  Some fonts have a
separate italic glyph that is very similar to the upright glyph,
and that is probably intentional because the font author thought
that the rendering of infinity should not depend on style.  Other
fonts have an italic glyph that differs.  So the rendering of
<mi>&#x221E;</mi> will depend on the font used.  Should authors
expecting an upright form always explicitly use

Many font rendering systems will produce an italic (or at least
oblique) variant of a character even when there is no
hand-constructed glyph, so there is almost always a visually
distinguishable italic character.  Or is there an expectation that
synthetic styles (either italic or bold) be suppressed and
only forms with glyphs from different font faces be used?

U+210F PLANCK CONSTANT OVER TWO PI is another interesting example.
U+210E PLANCK CONSTANT is a mathematical alphanumeric symbol but
U+210F is not.  Thus <mi>&#x210F;</mi> may end up with more slant
than <mi>&#x210E;</mi>.

One thing that concerns me is that, although we now have better
Unicode support for mathematical characters than ever, there seems
to be an increased expectation of creating characters by other
means that resemble style.
Received on Tuesday, 13 October 2009 20:40:55 UTC

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