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Re: Displaystyle and mtable

From: David Carlisle <davidc@nag.co.uk>
Date: Thu, 18 Sep 2014 16:07:44 +0100
Message-ID: <541AF540.7010202@nag.co.uk>
To: <www-math@w3.org>
On 17/09/2014 20:37, Peter Krautzberger wrote:
> Hi everyone,
>
> A follow-up question after Fred commented
> <https://github.com/dpvc/MathJax/commit/98e3f098bd519dabe9bf558736c5bf6438fbc217>
> on our changes to MathJax (following the results of this discussion);
> these changes include resetting the scriptlevel to 0. To us, this
> seemed to make the most sense after the discussion: if display style
> wasn't supposed to be inherited, then scriptlevel seemed strange to
> inherit (also, there were some "matching TeX behavior" comments on
> this thread).
>
> To put it differently, we couldn't imagine how an author setting
> displaystyle to "true" would expect to stay at scriptlevel=1 (for
> example). The only use-case we could think of would be an array in a
>  superscript or fraction, but this doesn't seem very likely.
>
> However, as Fred pointed out, the spec seems to read differently.
> Since displaystyle needed to be clarified, we thought it's best to
> ask for clarification on this as well.
>
> Thanks in advance, Peter.
>

I think the spec is clear, and the splitting of tex's \xxxstyle concept
into two separately settable parameters was certainly intentional:

3.1.6 says

> TEX's \displaystyle, \textstyle, \scriptstyle, and \scriptscriptstyle
> correspond to displaystyle and scriptlevel as "true" and "0", "false"
> and "0", "false" and "1", and "false" and "2", respectively.



That choice inevitably means that there are combinations not reachable
in TeX (and thus uncommon to most authors and probably unlikely
to be used except in exceptional circumstances) but I think it's clear 
that the spec intends that they are reachable.



David
Received on Thursday, 18 September 2014 15:08:18 UTC

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