Should sub-collections be able to repeat within a collection?

[elrayle]

coll1.collections = [coll2, coll3, coll2] # is coll2 twice ok?
if you append coll2 and it is already in the list of collections, should it be replaced/ignored?

see test: add_collection_spec.rb xit 'should allow collections to repeat'

same applies for hydra works collections

[escowles]

We've talked about repeating member objects, but I don't think I've heard a scenario for repeating member collections. Is there any reason not to allow it? If we have the ability to repeat objects, then repeating collections seems like it could follow the same pattern.