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[Bug 29670] [XSLT30] xsl:accumulator/ @initial-value accessing the global context item and streamability

From: <bugzilla@jessica.w3.org>
Date: Fri, 27 May 2016 18:24:53 +0000
To: public-qt-comments@w3.org
Message-ID: <bug-29670-523-Gg3yRamJYx@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=29670

--- Comment #4 from Abel Braaksma <abel.braaksma@xs4all.nl> ---
(In reply to Michael Kay from comment #3)
> Yes, let's just say that the global context item cannot be a streamed node.
> 
> Perhaps with a suggestion that when implementing a legacy API in which a
> single "setSource" method has provided both the GCI and the IMS, our
> recommendation is that when the supplied value is a streamed input source,
> and the initial mode is streamable, then the supplied value should be used
> to set the IMS, and the GCI should be absent.
With the current rules for xsl:global-context-item this would work, as the
default (if the declaration is absent) is type="item()" and use="optional".

This would then, of course, cause a dynamic (!) error if you would try to
access the GCI within xsl:variable/param etc, but that may be clearer than
requiring motionless expressions (and it does *not* remove the ability to have
the GCI set to a non-streamed document node, different from the IMS).

The only use-case we subvert is where the programmer wants information on the
input tree. But a workaround (which could go in a Note) is to use an
accumulator that only operates on the document node of the input tree.

What would happen if you access the GCI with a streamed accumulator, as in
comment 2? I think the answer should be: it doesn't matter, as a streamed
accumulator is equally applicable to non-streamed trees (but the inverse is not
true).

This would imply removing anything in the spec related to
xsl:global-context-item/@streamable="yes". Considering the issues we have with
"getting it right", I think that's a good thing ;). But is this an allowed
change at this CR stage?

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