Builder's Views and anything that's already a UIView are interchangeable. You can place any existing UIView directly into a VStackView (for example), and you can assign any Builder View to something that expects a UIView by simply calling .build() on it.

Builder is really just syntactic sugar on a UIKit view, plus some helper functions to allow SwiftUI-type view modifiers. Plus a few RxSwift integrations for reactive data binding.

The interoperability between View and UIView is what makes it easy to start using Builder in an existing app. (Which is sort of how it came into being in the first place.)