"""
The feed is an assembly of items of different content types.
For ease of querying, each different content type is housed in the FeedItem
model, which also houses metadata indicating the conditions under which it
should be included. So a feed is actually just a listing of FeedItem instances
that match the user's region and carrier.

Current content types able to be attached to FeedItem:
- `FeedApp` (via the `app` field)
- `FeedBrand` (via the `brand` field)
- `FeedCollection` (via the `collection` field)