wiki.trwnh.com/content/tech/spec/activitypub/gotchas/orderedItems.md

DO NOT CONFUSE ITEMS AND ORDEREDITEMS

items indicates that this is a Collection

however, orderedItems is valid on both Collection and OrderedCollection! it is defined like this in the as2 context:

{
	"orderedItems": {
		"@id": "as:items",
		"@type": "@id",
		"@container": "@list"
	}
}

so it is basically just an alias for items where it MUST be an array, and the array's order matters. (if it were @container: set, then it MUST be an array, but the array's order does not matter.)

tangent: a Collection may be ordered without being an OrderedCollection

OrderedCollection is defined as strictly reverse chronological by ActivityPub. however, other orderings are valid on regular Collections. the use of the orderedItems term allows plain-JSON implementations to do exactly this.