Major Description
Quoting Dan:
Collection changes have historically been supported, but they are mostly deprecated/removed for v2. Part of the rationale for that is the difficulty of defining what an "execution" would mean for them.
Historically there was "addToXxx" and "removeFromXxx" prefixes for a collection "getXxx". When we moved to building web UIs, this was somewhat difficult to express. In any case, it also makes sense to limit which objects can be added to or removed from a collection.
Thus, one would make the collection read only and then define actions that encapsulated the required business logic.
[... as] this stuff is only semi-deprecated, because you'll see that the RO viewer does define endpoints representing mutable collections, and the WrapperFactory also supports the notion. All this code could be removed [...]