startRegistryField

fun <T : Any, R : T> ConfigEntryBuilder.startRegistryField(
    fieldNameKey: Component, 
    value: T, 
    subclass: KClass<R>? = null, 
    registry: Registry<T>
): RegistryFieldBuilder<T, R>

See startSpecField. Builds a single registry-entry field, resolved against registry and optionally narrowed to subclass.