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Re: Implementation of semantics

From: David Carlisle <davidc@nag.co.uk>
Date: Tue, 30 Oct 2012 14:13:00 +0000
Message-ID: <508FE06C.7070306@nag.co.uk>
To: Frédéric WANG <fred.wang@free.fr>
Cc: www-math@w3.org
On 30/10/2012 13:54, Frédéric WANG wrote:
> Thank you for all your response. It seems that not everybody agree
> about the way semantics should be implemented

That's life:-)

> and one additional confusing aspect is that the intentionally
> simplistic Gecko implementation is used in practice.

Yes, irrespective of whether we decide a semantics element with only
annotations and no base should be valid, we should probably say
somewhere that in that case the first (or first usable?) annotation
should be used. So that the existing pages using this trick to make
mathml2-valid svg-in-mathml continue to work in browsers even if the
mathml3 schema continues to declare it invalid.

> So I guess Webkit and Gecko should try to do their best to implement
> a consistent behavior across browsers and perhaps the spec could be
> made more accurate.

Sounds like a plan.

> Regarding my fourth question, I think it does not really make sense
> either to take the presentation MathML to determine whether it is an
> embellished operator, when this element is not visible.

Yes I think that what should happen (although the spec is rather vague
here) is that if the system decides to use one of the annotations for
rendering rather than the base expression then the rendering should be
the same as if the chosen branch were the only thing there. (With some
suitable wording to be decided about the annotation-xml element being
replaced by mrow if the annotation is MathML and the fact that if the
annotation is some foreign markup it wouldn't be valid to actually just
have the foreign markup without the annotation wrapper.

> At least in Gecko, the embellished operator data passed to the parent
> also contain who should be stretched, so it's really relevant only if
> it is the operator is visible. So I think the correct behavior is to
> do as maction: the visible child is used to determine whether it is
> an embellished operator. Of couse, this only applied if the visible
> child is a presentation MathML. Also <maction> is space-like if the
> selected child is space-like and I guess that should be the same for
> <semantics>. Actually, I plan to share <maction> and <semantics>
> implementation in Gecko (both of them select one visible child after
> all) and so it would be best if the two behaviors were consistent.
> BTW, I guess <annotation-xml> should be said to behave as <mrow>, so
> that the embellished op data and "space-like-ness" are passed to the
> parent when <annotation-xml> is the selected child of <semantics>.

all sounds reasonable I think.


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