Transformation Reference

A 4-tuple identifying a published Transformation by its canonical URI: publisher + package + version + name. Used by other vocabulary packages (e.g. derivations) to point at a transformation without inlining or re-declaring it. The tuple resolves to a SubjectKanonak whose type is Transformation (concretely: InstanceTransformation or SetTransformation) when looked up against a repository. All four fields are required. Versionless references would defeat the point of the cross-package binding — if you don't pin a version, an upstream republish silently changes consumer behavior. Authors who want range-based version selection should encode that at a higher level (e.g. a publisher's site curation), not in the pointed-at reference.