Function container_value 

pub fn container_value<T: KeyValue>(
    view: &ViewHandle,
    key: &CustomContainerKey<T>,
    value: impl IntoKeyValue<T>,
) -> ViewHandle

.containerValue(\.key, value) for a key defined here.

What the @_alwaysEmitIntoClient modifier’s body does, since the modifier itself exports no symbol: build a _ContainerValueWritingModifier and apply it with .modifier(_:).