AtUri Type
An AT-URI that identifies a resource in the AT Protocol network.
AT-URIs use the scheme at:// followed by an authority (DID or handle),
an optional collection (NSID), and an optional record key.
Format: at://<authority>[/<collection>[/<rkey>]].
Maximum length is 8192 characters.
See the AT Protocol specification: https://atproto.com/specs/at-uri-scheme