A tweet by Jonathan Robie points out:
and
XQuery Update Facility 3.0 Requirements and Use Cases
have been issued as working group notes.
It’s not clear to me why anyone continues to think of data as mutable.
Mutable data was an artifact of limited storage and processing.
Neither of which obtains in a modern computing environment. (Yes, there are edge cases, the Large Hadron Collider for example.)
Still, if your interested, read on!