I am not sure if this is helpful, but a search got me this http://blog.mooregreatsoftware.com/
Part of that blog:
Sadly, the metadata files for AEM Package Manager are very, very poorly documented. To make matters worse, there is a lot of duplication and inconsistencies between them. There is a little bit of information at the Apache Jackrabbit FileVault Documentation site, but it is focussed at the Vault filesystem and the like, not specifically how to use packages. The Adobe 6.1 Package Manager documentation discusses creating a package through the UI, but doesn’t discuss any of the mechanics. The Maven VLT plugin talks a little about how to set up Maven, but has huge holes in what is actually done and what the values really mean.
In an effort to get some better understanding, I’ve done a lot of reading, testing, and reverse engineering to come up with the following information. If anyone knows where I can learn more, I’d love to know and pass that along!
Not sure if it completely talks about Apache Jackrabbit, but thought this might help.
And another one; talks about exporting data as XML
https://wiki.apache.org/jackrabbit/BackupAndMigration