InternalOptionalallowOptionalenforceOptionalforeignCTI-only: FK column name on the variant table that joins back to base PK.
OptionalrelationsVariant-scoped relations (already resolved to FK column names). When
the variant entry is sourced from another Entity, these are read
from that entity's 'relations' extension and passed in here.
Variant body schema (CTI table or STI extras).
Input to applyVariantsToSchema: a single resolved variant entry, as produced by
Entity.ctiVariant()/Entity.stiVariant().