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The node element with <code>@id=1</code> is copied and subsequently assigned a new QName using the rename expression. Note that the transform expression is the only expression which returns an actual XDM instance as a result. You can therefor therefore use it to modify results and especially DOM nodes. This is an issue beginners are often confronted with. More on this topic can be found in the [[Update#Returning Results|XQUF Concepts]] section.
The following example demonstrates a common use case:
So far BaseX differentiates between fragments and database nodes. Updates on fragments
have no effect on any existing databases and are therefore not applied at all. This
includes testing constraints as well. It is therefor therefore possible to execute an
update on a fragment, whereas the same update applied to a database node raises an error.
===DOM Nodes & fn:put()===
As a consequence, updates on a fragment are not visible in an a XML file created with
<code>fn:put()</code>. If this functionality is required, the transform expression can be applied.
The copied nodes in a transform expression are internally treated like database nodes
