Hi,
Could you indicate which sections you might find difficult to understand? I'll try to add more detail then.
There is also an old screencast that shows this in action, which is almost identical to how jBPM5 is using it (other than some small differences on how to create a new jBPM5 project):
http://people.redhat.com/kverlaen/DomainSpecificWorkItem.swf
Kris