Rendered from docs/obligations/0033-a-required-declaration-that-an-overlay-may-supply.md in the Headwater corpus. Every document on this half of the site is typed by the taxonomy the descriptor names: corpus.json.

A required declaration that an overlay may supply cannot be required of a source

Context

The meta-schema has one notion of a required member, and it holds a single source to it. Two of the facet acceptance tests need a second notion. A facet declares volatility, and every value of an enum carries guidance, and an overlay may supply either one at facets.status.volatility. So a base package that omits one is not yet wrong, and the resolved taxonomy that omits it is.

The engine runs both under taxonomy validate over the result, which is where spec 2 lists them.

Obligation

What stays open is the facet case and the vocabulary for it. volatility and guidance are optional members of the meta-schema, because the file has no way to say that a rule over the result requires them. So a reader cannot tell a member that nothing requires from one that taxonomy validate requires, and the two sit a line apart.

Discharge

The two new roots met this question and settled half of it. Every member of an obligation and of a control is required of the source that writes the entry. No source writes a partial entry. The meta-schema reads the value of an overlay operation against the shape at the address it names. The resolver refuses a remove of a required member.

The facet case differs because a base declares a facet and an overlay refines it. No adopter completes a publisher's obligation, and an adopter with a different invariant declares one of their own.