Type Alias ScreenTopOf<D>

ScreenTopOf: D extends { "~top"?: infer Marker }
    ? Exclude<Marker, undefined> extends ScreenTopLevelMarker<
        infer Top extends PropertyKey,
    >
        ? Top
        : never
    : never

The data fields a definition's handle shows on its top level (its main identifier), read from the definition's type-only ~top; none for a type that does not carry it.