How to Add Custom Sources to SourceSet?

I misunderstood your suggestion, I thought you were recommending I implement the SourceDirectorySet as demonstrated in the Groovy Plugin – hence the use of SourceDirectorySetFactory. Further, to confirm, as you mentioned in another post, I don’t have to implement the SourceDirectorySet in its entirety. Rather, I can define and implement an interface that includes only the APIs I am interested in, correct?