W3C home > Mailing lists > Public > www-math@w3.org > March 2006

Re: Technical reasons for some options taken on design of MathML

From: David Carlisle <davidc@nag.co.uk>
Date: Fri, 31 Mar 2006 15:29:20 +0100
Message-Id: <200603311429.k2VETKv7029835@edinburgh.nag.co.uk>
To: juanrgonzaleza@canonicalscience.com
CC: www-math@w3.org

> <apply><sqrt/>Content</apply>
> over something like
> <SQRT>content</SQRT>

there are advantages when you look at extensions.
you know immediately that that is a foobar symbol applied to 1 and
furthermore you do not need to extend the dtd to make that extension.
If every function had a special content model then the dtd is a lot less
flexible. (OpenMath takes a more extreme line than mathml here, some
content mathml do use special forms, but the general design aims are the

> I was not referring to the use of TeX syntax (which is not XML and
> therefore omitted in MathML). I was referring to the fact that *base* is
> outside of the “sup” tag in both SGML/HTML and TeX. That is, in TeX one
> does not write things as

the fact that TeX does not explictly mark the base of ^ expresions is a
real problem when converting TeX to anything else. You have to parse
back to find the base (and with TeX syntax that can never be more than a
guess). superscript is almost always denoting a 2 argument function
such as power(..,..), and it is far more natural to treat both those arguments
in a consistent way, making them both children. 

> if you have something like
> <msup><mi>a</mi><mi>b</mi><mi>c</mi><mi>d</mi></msup>
> what mean "((ab)^c)d" or "a(b^c)d" or something else? Also MathML syntax
> is ambiguous. This is reason that I carefully used an mrow example in my
> previous post

your example is a syntax error, so mathml would assign no meaning to it
and it would be rejected by a mathml syste,. msup may only have two
child elements and your example ha 4.

> Are there technical/conceptual advantages introducing the base into the
> script node or simply a matter of taste?

Many advantages. It makes the function application clearer, and it makes
it much easier to correctly position the superscrpt based on the size of
the base.


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Received on Friday, 31 March 2006 14:31:33 UTC

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