Proof-of-existence (proposed), poe/
Proof-of-existence records only need to store hashes of the actual data, e.g. an SHA256 of a document, image, sound or any other digital data. The registration process is the same as for d/ or id/ records. Updating is required every <36000 blocks (between 200 and 240 days) to be visible in the Namecoin blockchain explorers. Equally conceivable are applications that do not require updating records ("names" in Namecoin jargon). Expired names are still in the blockchain and can be used as a proof as long as we don't introduce blockchain purging.
All Namecoin transactions provide an inherent timestamping feature. Therefore proof-of-existence can also be used as proof-of-time-of-publication.