L2/01-064
From: Patrick D. F. Ion [mailto:ion@ams.org]
Sent: Wednesday, January 24, 2001 3:57 PM
Subject: Mathematical Variant Symbols
Dear Unicoders,
MathML has what could be a serious problem, and Unicode
has the means to obviate it in a way that I hope is in
full accord with the principles that have already been
applied in doing so much for the representation of mathematical
and scientific works.
The problem is a handful of math symbols that were not
accepted in the additional math set, because they were
held to be variants of others already accepted. That
is a perfectly commmon-place determination the UTC has
to make all the time. The symbols in question are
some LONG forms of arrows, which are certainly commonly
used in mathematical papers (the shorter forms would tend
to be used in connections with limits and the longer with
mappings, for instance). The problem arises because
their use is so common that they were assigned entities
in the ISOAMSA entity set, one of the several mathematical
symbol entity sets ISO defined.
MathML is an XML application, and MathML is intended to
support the full legacy collection of the ISO math entity
sets. This is at least in part because publishers who
use forms of the ISO 12087 standards for mathematics
would reasonably expect it to. The STIX project of the
STIPUB group of publishers naturally included those ISO
sets in its collection of mathematical characters from
which were drawn the big list submitted to the UTC for
consideration of possible additions.
Now, however, with the dust almost completely settled
over UCS characters for mathematics, in a way that will
be a boon to the community, the absence of the long arrows
poses MathML a problem.
There are several conceivable solutions, in increasing
order of desirability:
0. Ignore the problem
[unprincipled, and it would just bite us later]
1. Make assignments in the PUA for these symbols
[Back to the PUA at this stage seems absurd]
2. Make special markup arrangements in MathML for them
[a can of worms]
3. Use existing markup techniques to ensure explicit
sizes for these arrows
[possible, but then it raises questions of the explicit
sizing to be required. In addition, and more
importantly, it means that sharing character entity
sets with other XML applications, like XHTML, DocBook
etc. is not readily possible because one is not in
a position to resolve entities to anything but plain
text as a result of XML parsing. That leads to
difficulties getting MathML adopted we'd like to
finesse.]
4. Use the VS1 modifier to declare the longer forms
as variants of the corresponding shorter ones.
[This would solve the problem since it means any
possible character entity definitions would resolve
to plain text. The implementers of MathML have to parse
for VS1 and handle variant characters already. It
means no silly hacks to use these fairly common arrow
forms as math operators, which would result from
the markup solution. Generally it seems to have
few drawbacks.]
Therefore the W3C Math WG would like to urge the additoon
of the following items to the VS1 variant table:
[LONG LEFT DOUBLE ARROW]
[LONG RIGHT DOUBLE ARROW]
[LONG LEFT AND RIGHT DOUBLE ARR]
[LONG LEFT ARROW]
[LONG RIGHT ARROW]
[LONG LEFT AND RIGHT ARROW]
[LONG MAPS TO, LEFTWARD]
[LONG MAPS TO, RIGHTWARD]
Best regards,
Patrick
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