api/content/items responds with "model parameter missing"

[bomas13]

According to the playground, the /api/content/items endpoint should give me "a list of published model items".

First of all this endpoint responds with:

{
  "error": "<models> parameter is missing"
}

secondly, it might make more sense if it would return a description of the structure of the items that exist. Getting the items is already possible with the correct {model} parameter