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Re: [xsl] xsl:import and use-when


Subject: Re: [xsl] xsl:import and use-when
From: "Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 16 May 2014 07:58:24 -0000

On 16 May 2014, at 03:09, Abel Braaksma (Exselt) abel@xxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

>
> On 16-5-2014 2:49, Rushforth, Peter peter.rushforth@xxxxxxxxxxxxxxxxx
wrote:
>> With regard to statically known available documents [2], the spec says that
statically known documents [3] in the static context [4] are used to provide
static type information, not to determine which documents are available.  But
if a document is statically known, it is potentially available using the doc()
function, hence I think the use of doc-available() in use-when should be
legal, although if it isn't it isn't.
>
> You are quoting the XPath spec here, which allows enough breath for host
> languages to provide a list of statically available documents. However,
> in the section that you also refered to,
> http://www.w3.org/TR/xslt20/#conditional-inclusion, you should scroll
> down until the bottom of the first table, there is says:
>
> Statically known documents     None
> Statically known collections     None
>

Actually and rather confusingly, it's the "available documents" in the dynamic
context that matters, not "statically known documents" in the static context.
Use-when expressions (and in XSLT 3.0, other static expressions) are evaluated
during stylesheet analysis, so their dynamic execution occurs during the XSLT
static analysis (compilation) phase; their dynamic execution has a dynamic
context, and it is this that determines the results of doc() and
doc-available().

Saxon still implements the 2.0 restriction on using doc() in use-when
expressions, despite the relaxation in the spec. I can't see any particular
reason not to lift the restriction (which can be done by removing one line of
code and adding a load of test cases....). Oh, looking at it more carefully, I
see that there would be no document pool maintained across a compilation, so
multiple calls on doc() to fetch the same document would be grossly
inefficient.

Michael Kay
Saxonica


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