Composing native children

The magic word is Children()

How does <Host><HStack><Button/><Button/></HStack></Host> turn React children into native SwiftUI subviews? One function: Children(). Inside a SwiftUI-native view's body, calling Children() renders whatever React children were passed, as native views, right at that spot.

This is the whole composition model. A container view (an HStack, a VStack, a card) is just a SwiftUI layout whose body places Children() inside it.

In an interview, say: "@expo/ui composes native children through a Children() call in the SwiftUI body — React children are mounted as native subviews at that point in the layout. That's what lets you nest native controls declaratively from JS."