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[Bug 29696] New: [XSLT30] Dropping streamability of the global context item (GCI), in particular, xsl:global-context-item/@streamable

From: <bugzilla@jessica.w3.org>
Date: Thu, 16 Jun 2016 14:39:43 +0000
To: public-qt-comments@w3.org
Message-ID: <bug-29696-523@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=29696

            Bug ID: 29696
           Summary: [XSLT30] Dropping streamability of the global context
                    item (GCI), in particular,
                    xsl:global-context-item/@streamable
           Product: XPath / XQuery / XSLT
           Version: Candidate Recommendation
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: XSLT 3.0
          Assignee: mike@saxonica.com
          Reporter: abel.braaksma@xs4all.nl
        QA Contact: public-qt-comments@w3.org
  Target Milestone: ---

As a result of discussion in Bug 29670, and the follow-up discussion in
https://lists.w3.org/Archives/Public/public-xsl-wg/2016Jun/0000.html and
https://lists.w3.org/Archives/Public/public-xsl-wg/2016Jun/0001.html in the
public archive and a decision in the XSL WG meeting of 9 June 2016, I was
tasked with an action to create a bug report on dropping streamability on
xsl:global-context-item.

Reasoning:
The current rules do not allow you to move away from the beginning of the first
element of a GCI (any construct accessing the GCI must be motionless). As a
result, the GCI cannot be accessed past its head.

Fixing this (i.e., allowing reading the whole stream) proved very hard to write
down in spec rules.

Workaround:
The only use-case is getting information on the IMS (initial match selection)
in cases where IMS and GCI are the same. This can be circumvented by writing a
motionless accumulator that acts on the root node.

Decision:
The decision in the aforementioned XSL WG meeting was to drop this feature as
it seems to serve no practical purpose and the rules are complex. The parts of
the spec that needs updating are written out here:
https://lists.w3.org/Archives/Public/public-xsl-wg/2016Jun/0001.html.

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