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When to stretch parentheses

From: Vincent Quint <Vincent.Quint@inria.fr>
Date: Fri, 30 Jan 2004 11:36:30 +0100
To: www-math@w3.org
Cc: Vincent.Quint@inrialpes.fr
Message-Id: <20040130103630.2B1653D13@lihue.inrialpes.fr>

An user of Amaya reported recently an interesting case where Amaya and
Mozilla do not render an expression the same way. I checked the spec
and I am not sure how to interpret it to decide who is right.
Here is the case:

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mi>e</mi>
  <mo>(</mo>
  <mi>CM</mi>
  <mo>)</mo>
  <mo>=</mo>
  <mfrac>
     <mi>a</mi>
     <mi>b</mi>
  </mfrac>
</math>

In Amaya, the parentheses have the same height as the fraction, while
in Mozilla they are much smaller and have the same height as the
characters "CM" they enclose.

So, I checked the MathML 2.0 spec (2nd edition).

Section 3.2.5.8.2 of the MathML 2.0 spec (2nd edition) "Vertical Stretching
Rules", first bullet, says:
"If a stretchy operator is a direct sub-expression of an mrow element,
....then it should stretch to cover the height and depth (above and below
the axis) of the non-stretchy direct sub-expressions in the mrow element..."

I guess this is in favor of Mozilla: the stretchy operators are not
children of an mrow element, but children of a math element.

But, reading the spec further, section 7.1.2 "The Top-Level math Element",
3rd paragraph says:
"The math element can contain an arbitrary number of children schemata.
The children schemata render by default as if they were contained in an
mrow element."
(here, I suppose that "schemata" means "elements", and that "children"
means the same as "direct sub-expression" in section 3.2.5.8.2).

This seems to be in favor of Amaya.

Is my reasoning right? Or should Amaya do the same as Mozilla?

I should add that if you introduce an mrow element as a child (or
direct sub-expression) of the math element, to enclose all the contents
of the original math element, both Amaya and Mozilla do the same: they
display large parentheses.

Thanks for any advice,

Vincent.

-------------------------------------------------------
Vincent Quint                       INRIA Rhône-Alpes
INRIA                               ZIRST
e-mail: Vincent.Quint@inria.fr      655 avenue de l'Europe
Tel.: +33 4 76 61 53 62             Montbonnot
Fax:  +33 4 76 61 52 07             38334 Saint Ismier Cedex
                                    France
Received on Friday, 30 January 2004 05:37:52 GMT

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