This is one of many protocol behaviors described in ActivityPub.

Identifier

urn:uuid:abef3a0a-d3c4-4dee-a320-b28837d0bcd8

Content

The followers collection MUST be either an OrderedCollection or a Collection

Origin

prefix Every actor SHOULD have a followers collection. This is a list of everyone who has sent a Follow activity for the actor, added as a side effect. This is where one would find a list of all the actors that are following the actor.

The followers collection MUST be either an OrderedCollection or a Collection
 
suffix and MAY be filtered on privileges of an authenticated user or as appropriate when no authentication is given.

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

JSON

{
  "id": "urn:uuid:abef3a0a-d3c4-4dee-a320-b28837d0bcd8",
  "type": "Behavior",
  "uuid": "abef3a0a-d3c4-4dee-a320-b28837d0bcd8",
  "content": "The followers collection MUST be either an OrderedCollection or a Collection",
  "origin": {
    "source": "https://www.w3.org/TR/activitypub/",
    "section": {
      "id": "https://www.w3.org/TR/activitypub/#followers",
      "branch": [
        5,
        3
      ]
    },
    "selector": {
      "type": "TextQuoteSelector",
      "prefix": "Every actor SHOULD have a followers collection. This is a list of everyone who has sent a Follow activity for the actor, added as a side effect. This is where one would find a list of all the actors that are following the actor.\n",
      "exact": "The followers collection MUST be either an OrderedCollection or a Collection\n",
      "suffix": "and MAY be filtered on privileges of an authenticated user or as appropriate when no authentication is given.\n"
    }
  },
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://socialweb.coop/ns/testing/context.json"
  ]
}