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Date:         Tue, 20 May 2014 09:19:30 -0400
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From: Barbara Beeton <bnb@AMS.ORG>
Subject: Re: Unicode math
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Status: R

On Tue, 20 May 2014, Joseph Wright wrote:

    [...]

    > In contrast, Unicode math defines a number of alphabets in a single Unicode
    > font, including mathematical italic and bold mathematical italic and many
    > more variations. In OpenType maths fonts to date, these symbols are all
    > designed as single-letter identifiers and not to be used for strings of
    > characters such as "Re" in italic or "Set" in bold.

    To be clear, the Unicode position is that e.g. bold-B for magnetic field
    should not come from the 'bold' font but from the bold-symbols part of a
    single maths font: correct? That being the case, have the Unicode people
    considered at all multi-letter identifiers or has this simply been
    missed at present? (Anyone on the list sufficiently well-informed about
    this?)

having been the stix representative to
the unicode technical committe, i hope
that i'm sufficiently well-informed.

the unicode people didn't consider
multi-letter identifiers specifically,
since only single letters are (normally)
given character status.  as pointed out
(i think by david), one goal of the
alphanumeric block in plane 1 was to
be able to drop single characters into
text and have them recognized as math
identifiers (one of the "math subgroup"
was murray sargent of microsoft, who
has been responsible for the ms work
adding math to office).  another
explicit goal was to be able to search
for individual math expressions by
unicode to find in what documents a
particular identifier had been used.
explicitly *un*intended was the
ability to easily use, say, fraktur
or script for wedding invitations,
hence the location in plane 1.

the unicode goal is to have only one
code per "meaning".  hence the absence
of the "usual version" of an alphabet
(usually upright lightface) from the
plane 1 math block.  (the absence of
lightface sans greek is an oversight;
this has been resubmitted, with a
reference to nist special publication 811,
  http://physics.nist.gov/cuu/pdf/sp811.pdf
page 22, where lightface sans is used,
though not by name, in the definition
of the *dimensions* of si base quantities.
one greek letter, theta, is shown; not
sure whether the theta is upper- or
lowercase, but it's the principle
that's important to the utc.)  more
information (and history regarding the
deciding example that resulted in the
inclusion of the plane 1 alphanumeric
block) is given in unicode tech report #25:
  http://www.unicode.org/reports/tr25/

regarding identifiers, see utr#25, in
particular sections 2.16 and 4.4.  (the
latter section does strongly hint that
the characters in the plane 1 block can
be used for multi-letter identifiers.)

hope this is helpful.
						-- bb