W3C home > Mailing lists > Public > public-xml-core-wg@w3.org > June 2009

[David Carlisle] Re: question about xlink 1.1

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Wed, 24 Jun 2009 16:20:54 +0100
To: public-xml-core-wg@w3.org
Message-ID: <f5br5x97j55.fsf@hildegard.inf.ed.ac.uk>

attached mail follows:



Henry,

I don't think I can post to public-xml-core-wg but a comment on

http://lists.w3.org/Archives/Public/public-xml-core-wg/2009Jun/0030.html


> However, I am left with one residual query in this area:  why isn't
> href #REQUIRED in simpleAttrs in the DTD (and schemas)?  Why does the
> spec. say "it MAY be used on simple-type elements"?  What does a
> simple link w/o an href mean?

a dtd fragment using #IMPLIED  is more useful than one using #REQUIRED
for many uses of xlink (and for similar reasons the dtd shouldn't
default a type="simple" attribute, now that xlink 1.1 doesn't require
one.


Consider for example MathML2 where every element can be used as a link,
by using xlink:href attribute. It's useful to be able to include a dtd
fragment that sets up #IMPLIED xlink attributes so that this usage is
DTD valid but you can't _require_ href on every element.

Defaulting type="simple" is slightly different. xlink 1.0 mandated use
of type attribute so mathml originally defaulted type="simple" in the
dtd which looked fine from an authoring point of view, but we got very
negative feedback from mozilla (in particular) because if they used a
dtd that defaulted this attribute it was really there in the DOM on
every element and in a markup heavy language like mathml that is a heavy
cost, especially if the majority of documents are not using xlink at
all.  So at some point we changed the dtd not to default type="simple"
which meant it had to be explict on every link. So xlink 1.1 not
requiring this would be a good thing, but not using a dtd that defaults
the attribute again.


Feel free to forward or discard as you see fit:-)


David

________________________________________________________________________
The Numerical Algorithms Group Ltd is a company registered in England
and Wales with company number 1249803. The registered office is:
Wilkinson House, Jordan Hill Road, Oxford OX2 8DR, United Kingdom.

This e-mail has been scanned for all viruses by Star. The service is
powered by MessageLabs. 
________________________________________________________________________





-- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
                         Half-time member of W3C Team
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
[mail really from me _always_ has this .sig -- mail without it is forged spam]
Received on Wednesday, 24 June 2009 15:22:17 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 24 June 2009 15:22:18 GMT