You at least parse the document, process it, and serialize some result: that's three steps.

Parsing and serialization are somewhat implicit in most systems.

A better example is schema validation:

• Schema validation adds information to the infoset (e.g. type names, validity flags, etc.).

• Schema processing before an application component would give an application component more information.

• Based on whether that document is valid or not, you might do different things.

There are lots of component specifications:

• XML Schema

• XSLT, XPath, XML Query

• XPointer, XLink

• XML Base, XInclude

• SOAP

• etc.