Makes certain kinds of programs really easy:
Filter out certain kinds of nodes
Filter out certain tags
Convert processing instructions to elements
Comment reader
Change names of elements
Add attributes to elements
Changes have to be local to be easy:
Start-tag changes based on name, namespace, and attributes
End-tag changes based on name and namespace
Event changes based on that event only
No direct filtering support
I don't know whether these programs are realistic patterns or just common tutorial examples