JAXB
 - Not that well known or used
 - Was part of Java, now Jakarta EE
 - Can be a bit inflexible
 - Uses Annotations to Unmarshall to POJOs

StAX
 - Very Efficient
 - Pain to write data out again
 - Simple

Dom4j/Generic DOM lib
 - Wildly inefficient
 - Not particularly correct
 - Simple
 - Slightly poor docs (dom4j)

XOM
 - Reasonably Efficient
 - Very Flexible - extend and override
 - Not that well known
 - Fairly simple
 - Unmarshals XML to Objects via factories.
 - Designed by a single well-respected author

Added XOM to a test app and investigated. Seems to work well, and the extensive documentation and demo is very helpful.

**Validation**
Checked XOM Docs for validation information. Copied the validating Demo into a test project; didn't work initially, but did after checking the Xerces docs and fixing Java Module issues.
Seems fairly simple to use internal schema documents.




      David