The support for the invocation of dynamic functions is another feature that is only supported since version 3 of the specification. To be strict, the finalized version of the spec woud require the "updating" keyword to be prepended by an additional "invoke" keyword [4].
Thanks for your detailed feedback.
How will the available software evolve further also according to information like “BaseX offers a complete implementation of the XQuery Update Facility (XQUF).”?
Regards, Markus