If you limit membership for each challenge (eg, for a gift exchange), people can sign
up for each subcollection separately. If you just want the whole thing moderated, have people sign up as members of the parent collection; they'll then be able to post in every subcollection.
- Note: Collection settings do not apply to works until they have been approved by the moderator and added to the collection. As a result, a work will be visible until it is added to the collection. The author's name will also remain attached to the work even if the collection is set to anonymous.