==XQUF Concepts==
There are a few specialties around XQuery Update that you should know about. In addition to the '''simple expression''', the XQUF adds the '''updating expression''' as a new type of expression. An updating expression returns only a Pending Update List (PUL ) as a result which is subsequently applied to addressed databases and DOM nodes. A simple expression cannot perform any permanent changes and returns an empty or non-empty sequence.
===Pending Update List===