Hi Gunnar,
Thanks for taking a look at this. The use case is as follows:
In general, it is a chain of command pattern with processors at each link. The processors all realize a single interface with a process method. The process method takes a single parameter, the processors may add or change the parameter properties. Subsequent processors require these properties to be non-null. Rather than implement this within the mainline code, I'd prefer to annotate with NotNull and NotNullProperty (a constraint and validation that I wrote).
I could do this with groups but that makes the connection between the expected properties and the annotation one step removed i.e. developers would have to know the definition of the group.

thanks