Daniel,
It would be much easier for you if you migrate code to use ResourceDefinition/AttributeDefinition that way you won't need to write DescriptionProvider by hand.
Most subsystems in as7 have already been migrated(as of current master), as the old approach was(is) too error prone.
We are currently in process of migrating everything to ResourceDefinition and by time of 7.2 is released everything will be migrated.
you can check Mail, ModCluster, Pojo,web subsystems to see how it is used.
The guide,sample subsystem and archetypes ware updated for 7.1.1 to show how this is used.
https://docs.jboss.org/author/display/AS71/Extending+JBoss+AS+7
There are also some other examples how to better write subsystems.
if you need any help, you can write here or ping us on irc #jboss-as7
--
tomaz