The Watchlist Service powers the 'Add to Watchlist' action and related experiences for authenticated consumers. Video publishers can allow registered consumers to save videos for watching at a later time. Supported Watchlist API operations include managing watchlists (create, update, delete, retrieve), and managing their associated videos (add, update, delete, retrieve).
Default Watchlist and Additional Watchlists
Every user has a default watchlist that the Watchlist Service automatically creates for them. The name attribute for this watchlist is set to "default". A client application can update items on the default watchlist simply by omitting the watchlist_id in the API request.
A client application can, optionally, create additional watchlists per user. The Watchlist Service assigns a unique watchlist_id when a watchlist is created. The client application provides this watchlist_id in subsequent API calls.
Watchlist Items (Videos)
Each watchlist can contain zero or more items (videos).