Modifications that you specify as a part of an update query are not actually made until after the query is completed. The order in which update statements are made may or may not be relevant when it comes time to apply the update. As a result, it's possible to request an update that on its own is acceptable, but when used with other update statement may result in an error.

Keep the following rules in mind as you use update expressions:

1. An exception is raised if:
   • two or more rename expressions target the same node
   • Two or more replace expressions or replace value of expressions target the same node
2. The following expressions are made effective, in the following order:
   • All insert into, insert attributes and replace value expressions in the order they are supplied.
   • All insert before, insert after, insert as first, and insert as last expressions in the order they are supplied.
   • All replace expressions
   • All replace value of expressions
   • All delete expressions

Note that atomicity of the expression is guaranteed; either the entire expression is made effective with regard to the original document, or no aspect of the expression is made effective.