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Re: Help: use-when and p:episode

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Wed, 11 Nov 2009 10:46:42 +0000
To: Norman Walsh <ndw@nwalsh.com>
Cc: public-xml-processing-model-wg@w3.org
Message-ID: <f5b1vk5e3u5.fsf@hildegard.inf.ed.ac.uk>
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Norman Walsh writes:

>> I now actually think that in its present form, use-when is
>> underspecified. A the moment, the spec says that use-when "must contain
>> an XPath expression that can be evaluated statically". But what does
>> that really mean? How does that affect XPath extension functions like
>> p:step-available(), p:value-available() etc.?
>
> It means that the expression cannot make any reference to the context
> node, position, or size.

I think we can go further without either reducing usefulness or making
life impossible for implementors, along the following lines: Come up
with an obvious minimum list of functions which make sense for use in
use-when expressions (suggested starting point below), and say that
use of any _other_ functions will give implementation-determined
(i.e. unreliable) results.

Candidate list of OK functions/sub-cases:

 * p:system-property
      p:language
      p:product-name
      p:product-version
      p:vendor
      p:vendor-uri
      p:version
      p:xpath-version
      p:psvi-supported
 * p:step-available
      [for built-in steps (p: and extension) only]
 * p:base-uri
      [no arg possible]
 * p:resolve-uri
 * p:version-available
 * p:xpath-version-available

That's it.

Perhaps the easiest way to do this is to mark these with some marginal
symbol in section 2.7. . .

ht
- -- 
       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]
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Received on Wednesday, 11 November 2009 10:47:19 GMT

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