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Re: stretching in both directions [was Operator Dictionary MathML 2 vs. MathML 3]

From: David Carlisle <davidc@nag.co.uk>
Date: Thu, 24 Sep 2009 10:11:28 +0100
Message-Id: <200909240911.n8O9BSxk012279@edinburgh.nag.co.uk>
To: w3@karlt.net
Cc: www-math@w3.org, fred.wang@free.fr, neils@dessci.com

> If I am reading the spec correctly, the follow vertical arrow should
> stretch both horizontally and vertically.
>  <mo stretchy="true">&UpArrow;<mo>

As the stretching defaults are system defined, it would (just about) be
conformant behaviour if did that but it would be contrary to expectations
and pretty unhelpful. The expectation is, as it says in the text you
quoted, that characters are marked as stretching in at most 1 direction
in almost all cases. So vertical arrows should just stretch vertically,
otherwise they are unusable.

> When stretchy="true" is not explicitly specified, I'm imagining an
> implementation that only stretches in the expected direction by
> having the renderer choose which directions to stretch by default
> based on the operator.

If an implementation sets stretch=true as the default in its operator
dictionary, use of the character with stretchy="true" should be the same
as use without the stretch attribute.

> But should I be concerned about unexpected behavior if
> stretchy="true" is explicitly specified?

Yes, it shouldn't happen!

> Should the renderer be expected to keep of list of all the
> operators that it will respect the stretchy request and in which
> directions it will respect the request?


(personal response not checked with the WG, we have a phone conference
this afternoon, I'll get thsi added to the eagenda...)

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Received on Thursday, 24 September 2009 09:12:07 UTC

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