From: Jim Allan (jallan@smrtytrek.com)
Date: Mon Jun 02 2003 - 17:21:33 EDT
Rick McGowan asked:
> Can someone point more specifically to where it says anything about
> variation selectors? This pointer is to the table of contents/overview...
Well, at
http://www.usefulcontent.org/docs/manuals/REC-MathML2-20010221/chapter6.html#chars_mathmlchars
I find:
<< This specification of MathML makes use of some characters that are
not part of Unicode 3.0 but which have been proposed to the Unicode
Technical Committee (UTC), and thus for inclusion in ISO 10646. They are
presently expected to be in the revisions Unicode 3.1 and 3.2. (For more
detail about this see Section 6.4.4 [Status of Character Encodings].)
While the process of review and adoption by UTC and ISO/IEC of the
characters of special interest to mathematics and MathML is largely
complete (Unicode Work in Progress) there remains the possibility of
some further modification of the lists of characters accepted, of the
code assignments for those adopted, or of the names given them by
Unicode. To make sure any possible corrections to relevant standards are
taken into account, and for the latest character tables and font
information, see the W3C Math Working Group home page and the Unicode
site. >>
This indicates we are dealing with a fairly old and tentative
recommendation.
Later:
<< 6.3.5 Variant Mathematical Characters
Unicode attempts to avoid having several character codes for simple font
variants. For a code point to be assigned there should be more than a
nuance in glyphs to be recorded. To record variants worth noting there
is a special character proposed for Unicode 3.2, U+FE00 (VARIATION
SELECTOR-1), which acts as a postfix modifier. However the legally
allowed combinations with this variation selector are restricted to a
list recorded as part of Unicode. The VARIATION SELECTOR-1 character may
only be applied to the characters listed here. The resulting combination
is not regarded by Unicode as a separate character, but a variation on
the base character. Unicode aware systems may render the combination as
the base if the available fonts do not support the variant glyph shape. >>
At the bottom of the page:
<< The additions accepted are expected to be published as an amendment
to [ISO/IEC 10646-1], and to become part of Unicode 3.2. It can
therefore be expected that almost all of the characters in this category
will finally be accepted, and encoded at the current code points. It is
possible that a small number of characters may be renamed, moved, or
less likely, ultimately rejected. There is even a handful of characters
which have still Private Use Area codes in our tables; even these it is
hoped will finally be fully recognized. Until final acceptance,
implementers and users of MathML are using these characters and code
points at their own risk. Entities and the mathvariant attribute are
used to avoid that risk. >>
Variants that are part of the recommendation appear at
http://www.usefulcontent.org/docs/manuals/REC-MathML2-20010221/variants.html
including the slashed zero glyph.
It would seem that the slashed zero variant was either not actually
included in the variants eventually proposed or was not accepted or
(barely possible) was somehow lost and forgotten about.
But the recommendation is quite clear about the tentative nature of its
presentation.
Jim Allan
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