This mixin enables a class to host controllers.
This enables controllers to be added to the life cycle of this element.
Internal storage uses TypeScript private + lazy ??= initialization — the
same pattern Lit's ReactiveElement uses for its own ReactiveController list.
This allows addUmbController to be called during addInitializer
callbacks (which run before subclass class-field initializers), mirroring
Lit's behavior.
This mixin enables a class to host controllers. This enables controllers to be added to the life cycle of this element.
Internal storage uses TypeScript
private+ lazy??=initialization — the same pattern Lit's ReactiveElement uses for its own ReactiveController list. This allowsaddUmbControllerto be called duringaddInitializercallbacks (which run before subclass class-field initializers), mirroring Lit's behavior.