[Bug 19425] New: [XP30] Substitution group membership is non-transitive

https://www.w3.org/Bugs/Public/show_bug.cgi?id=19425

          Priority: P2
            Bug ID: 19425
          Assignee: jonathan.robie@gmail.com
           Summary: [XP30] Substitution group membership is non-transitive
        QA Contact: public-qt-comments@w3.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: mike@saxonica.com
          Hardware: PC
            Status: NEW
           Version: Last Call drafts
         Component: XQuery 3.0
           Product: XPath / XQuery / XSLT

In discussing subtype judgements, we say in rule 17 of 2.5.6.2 that Ai is a
subtype of Bi if:

Bi is schema-element(Bn), the expanded QName of An equals the expanded QName of
Bn, Ai is schema-element(An), and either the expanded QName of An equals the
expanded QName of Bn, or the element declaration named An is in the
substitution group of the element declaration named Bn.

In other words we are saying that if E is in the substitution group of B and B
is in the substititution group of A, then E is in the substitition group of A.

I don't think this is necessarily true. For example if A and B have the same
type, and if the type of E is derived by extension from this type, and if A
blocks extension but B does not, then B is in the substitution group of A, E is
in the substititution group of B, but E is not in the substitution group of A.

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