Plain English
Schemas check whether a message has the right shape before anyone interprets its meaning.
Technical summary
They require fields such as profile, UAI target version, locale, normalization, registry, and payload, then leave semantic interpretation to registry and validator layers.
Deep spec
A schema cannot prove semantic correctness by itself. It proves structure; registry lookup and validation prove whether a compact mapping is acceptable for the declared profile.
Schema jobs
- Reject missing required metadata.
- Separate readable source forms from compact export forms.
- Preserve validator reports as evidence instead of hidden state.
- Allow future server-side validators without changing the page structure.