We recommend setting the playlist value to a URL containing the list of media items contained in the playlist unless you have a unique use case, such as creating a playlist from externally-hosted (non-JWP) media that is not in a feed.
We recommend setting the playlist value to a URL containing the list of media items contained in the playlist unless you have a unique use case, such as creating a playlist from externally-hosted (non-JWP) media that is not in a feed.