This is one of many protocol behaviors described in ActivityPub.

Identifier

urn:uuid:9cadac35-6926-4359-b5d3-32a74d038131

Content

clients submitting the following activities to an outbox MUST also provide the target property: Add, Remove.

Origin

prefix Clients submitting the following activities to an outbox MUST provide the object property in the activity: Create, Update, Delete, Follow, Add, Remove, Like, Block, Undo.

Additionally, clients submitting the following activities to an outbox MUST also provide the target property: Add, Remove.
 
suffix 6.2 Create Activity

https://www.w3.org/TR/activitypub/

JSON

{
  "id": "urn:uuid:9cadac35-6926-4359-b5d3-32a74d038131",
  "uuid": "9cadac35-6926-4359-b5d3-32a74d038131",
  "type": "Behavior",
  "content": "clients submitting the following activities to an outbox MUST also provide the target property: Add, Remove.\n",
  "context": [
    "https://www.w3.org/TR/activitypub/",
    {
      "name": "Client to Server interactions",
      "id": "https://www.w3.org/TR/activitypub/#client-to-server-interactions"
    },
    {
      "name": "Client Addressing",
      "id": "https://www.w3.org/TR/activitypub/#client-addressing"
    }
  ],
  "origin": {
    "source": "https://www.w3.org/TR/activitypub/",
    "section": {
      "id": "https://www.w3.org/TR/activitypub/#client-addressing",
      "name": "Client Addressing",
      "branch": [
        6,
        1
      ]
    },
    "selector": {
      "type": "TextQuoteSelector",
      "prefix": "Clients submitting the following activities to an outbox MUST provide the object property in the activity: Create, Update, Delete, Follow, Add, Remove, Like, Block, Undo.\n",
      "exact": "Additionally, clients submitting the following activities to an outbox MUST also provide the target property: Add, Remove.\n",
      "suffix": "6.2 Create Activity\n"
    }
  },
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://socialweb.coop/ns/testing/context.json"
  ]
}