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The spec says: [ERR XTDE0041] It is a dynamic error if the invocation of the stylesheet specifies a function name and arity that does not match the expanded QName and arity of a named stylesheet function defined in the stylesheet, whose visibility is public or final. Many of the tests in the initial-function test set fail to declare the visibility of the initial function, which is therefore private by default. I shall change these tests to use visibility="public" and add a new test for the error case.
I think these tests were written in the time that the default of declarations was public, when the visibility attribute was absent. I agree with your proposal for fixing it, tx.
Related: #30398 and spec bug #30401. Tx for the fix. Closing this bug, as it has been fixed for a while now.