perkeep/doc/schema/keep.md

Keep Object

A signed "keep" edge for GC/indexing purposes. Expresses a user's intent to keep an object.

This is not the only way to keep an object alive for the purposes of GC. Permanodes (signed by a user) are also part of that user's roots, and anything they reference (including blobs via "become" claims on those permanodes)

This is just the most explicit way when you're not modeling the data with permanodes.

{"camliVersion": 1,
 "camliType": "keep",
 "target": "digalg-blobref-of-thing-to-keep",
<REQUIRED-JSON-SIGNATURE>}