SceneTokenDecl.export constructor
An export: the app's own value, named and typed, never read. The type
decides where the editor offers it — a Color on colour properties, a
TextStyle in a text's style slot, a double on numbers — and
anything else is OPAQUE: only an external widget's argument of that
type can take it. The guest resolves the name; the editor never holds
the value, so an export binding is never auto-detached.
Implementation
SceneTokenDecl.export(this.name, this.type)
: owner = SceneTokenOwner.export,
kind = _exportKinds[type],
value = null,
_styleType = _exportStyleTypes.contains(type);