W3C home > Mailing lists > Public > www-math@w3.org > June 2014

Re: Displaystyle and mtable

From: Davide P. Cervone <dpvc@union.edu>
Date: Thu, 12 Jun 2014 07:50:22 -0400
Cc: David Carlisle <davidc@nag.co.uk>
Message-Id: <F15D5A3E-EA2C-4E31-B0BA-E6890F5433EA@union.edu>
To: www-math@w3.org
> The part that seems inconsistent to me is 
> 
>  "They also may be set explicitly via the displaystyle and
>  scriptlevel attributes on the mstyle element or the displaystyle
>  attribute of mtable. In all other cases, they are inherited from
>  the node's parent."
> 
> because "explicitly" here also applies to "displaystyle
> attribute of mtable", and "all other cases" seems to imply that
> the previous sentences form an exhaustive list.
> A default (not explicit) attribute of mtable was not in the
> exhaustive list.

Yes, that is certainly a source of the inconsistency in my mind as well.

> Perhaps removing "explicitly" might be enough to remove the
> inconsistency.

Yes, that would help, and David's suggestion of adding mtable to the list of elements that modify the displaystyle setting in the sentence before that would also help.  Although David indicates that this is not an exhaustive list, it appears to be an exhaustive list, particularly when the "all other cases" is taken into consideration.  Even the parenthetical statement about seeing the particular element's descriptions could be read to refer to the elements in the list just given.  The fact that mtable has a special rule for displaystyle puts it in the same category as mfrac, mroot, and the script and limit tags.  I guess the only other one not listed is mscarries, unless that is considered a scripting tag.  So adding mtable (and perhaps mscarries) would make it an exhaustive list.

The fact that the default in the attribute list for mtable is set to "false" and not "inherited" is also not enough to prevent misunderstanding (as mstyle overrides lots of attributes that don't have default of "inherited") without a very careful reading of a complicated ruleset that is described in several different locations in the specification.  Displaystyle in particular is unusual in that it has values for each element, but can only be set via the <math> or <mstyle> tags, or the <mtable> tag.  So the "special rules" that apply to <mfrac> and <mroot> aren't a problem, because you can't specify displaystyle on these directly (so there is no ambiguity about what value of displaystyle is in effect and how that propagates to the children).  On the either hand, since <mtable> can have a displaystyle attribute, a surrounding <mstyle> should be able to set that value, just as it does for any other attribute of its children.  The exceptions are listed in the 9th paragraph of section 3.3.4.1 (counting the bullets as paragraphs), and displaystyle for mtable is not listed among them.  Perhaps it should be.

Davide
Received on Thursday, 12 June 2014 11:50:51 UTC

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