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Re: default for ma@symmetric

From: David Carlisle <davidc@nag.co.uk>
Date: Sun, 09 Feb 2014 02:12:37 +0000
Message-ID: <52F6E415.9050504@nag.co.uk>
To: www-math@w3.org
On 09/02/2014 01:34, Davide P. Cervone wrote:
> Neil:
> Thanks for your comments, as always.
>> The operator dictionary only lists a value when the value is true
>> -- if a value isn't given and it is relevant, then it's value is
>> false. There is some text a few paragraphs above that explain
>> that.
> The text says
> "Boolean valued attributes such as stretchy are specified together
> in the final *Properties* column by listing the attribute name if
> its value should be set to *true* by the dictionary.
> Any attribute not listed for some entry has its default value, which
> is given in parentheses in the table of attributes in Section 3.2.5
> Operator, Fence, Separator or Accent <mo>"
> which is why I wanted to understand the default better.  This seems
> to say that when the value is true when it is listed, and the
> default value otherwise.  (Presumably, this would be false.)  It is
> not clear how to specify a false property when the default is true
> (though I would think symmetric=false would be one way, based on the
> non-boolean properties listed in that column).
> In any case, I'm afraid it is still not clear to me.  It would have
> made sense to have had the property column work as you suggest, but
> that doesn't seem to be what is documented.
> Davide

All the boolean attributes other than symmetric default to false, so in
the operator dictionary interpreting the lack of the property name as
the default or as false comes to the same thing.

For symmetric, now it's clarified as defaulting to true, as written an
operator dictionary _could_ set it to false but the compressed notation
used in appendix C can not express that and so in fact they are all true
and "symmetric" in the table no effect other than a visual hint in the
sample dictionary.

An alternative would be to say that an omitted boolean property name
means false, but then we would have to check whether it needs adding
to more entries eg the vertical arrows which are the majority of
vertically stretchy characters for which currently symmetric isn't
explicit in the table.

Received on Sunday, 9 February 2014 02:13:05 UTC

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