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The expression in the value attribute is
essentially an anonymous function -
<account-total value="fn(){29 + 12 * 1.25}"/> In the current implementation of XPath, there is no mechanism to enable the evaluation of anonymous functions, because that's a second order operation. There is some discussion in the XQuery 1.1 spec about working with higher functions, I'd have to dig into it a bit in order to tell you precisely where, however. You won't find it in the current public documents. A
detailed proposal for higher-order functions in XQuery has been accepted by the
Working Group (it adds "function" to the data model as a third kind of item,
alongside nodes and atomic
values), and it is implemented in Saxon 9.2 which is now in a limited beta
release, but the spec has not yet found its way into a public draft. There are
still decisions to be made about whether and how to expose the functionality in
XSLT/XPath.
Of course dynamic XPath evaluation has been available in
XSLT processors, as a vendor extension, for years.
Regards,
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