public-message.json

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Create",
  "id": "https://social.example/alyssa/posts/9282e9cc-14d0-42b3-a758-d6aeca6c876b",
  "to": ["https://social.example/alyssa/followers/",
         "https://www.w3.org/ns/activitystreams#Public"],
  "author": "https://social.example/alyssa/",
  "object": {
    "type": "Note",
    "id": "https://social.example/alyssa/posts/d18c55d4-8a63-4181-9745-4e6cf7938fa1",
    "attributedTo": "https://social.example/alyssa/",
    "to": ["https://social.example/alyssa/followers/",
           "https://www.w3.org/ns/activitystreams#Public"],
    "content": "Lending books to friends is nice.  Getting them back is even nicer! :)"
  }
}