At this point, we have read, parsed, transformed, and used XML in a variety of formats. We have used XML for content and presentation, for procedure calls across a network, and for telling an application how to behave on startup and execution. Next, we complement this store of reading and using XML with writing XML. In Chapter 12, we look at the other half of XML handling, mutability. This will round out your XML toolbox to include the ability to have your applications generate XML documents at runtime, often changing the inputs of other application components.