I read the schema struct. That's when I understood what Sign Protocol is actually built on. Most developers skip the data structures. I don't. A Sign Protocol schema is a registered on-chain struct containing the registrant address, a revocable flag determining whether attestations using it can be revoked, a data location field, a maxValidFor expiry parameter, an optional hook contract for custom validation logic, and the schema data itself. That `maxValidFor` field stopped me. Built-in expiry at the schema level means credentials don't require manual revocation to become invalid. They age out by design. The hook contract is the other detail worth noting. Custom validation logic attached directly to schema registration means enforcement rules travel with the data format itself. That's not a data standard. That's a data standard with programmable consequences. The difference is significant.

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