Optional ReadonlyoccurrenceOccurrence ids the reopened hierarchy actually carries, when known.
Optional ReadonlypackageReadonlypackageFalse when the package could not be opened at all.
Optional ReadonlyresourcesOptional ReadonlyresourcesTrue when resources is the reopened package's complete resource list.
Readonlysourceunavailable means the host cannot inspect sources, not that none moved.
Optional Readonlysources
What the host managed to see. A browser can always verify the package it just loaded; it can verify a source only when the embedder grants a source-inspection capability, which is why the two halves are separate.