Consider these SwiftUI signatures:

toolbarBackground(_: Visibility, for: ToolbarPlacement...)
toolbarBackground(_: any ShapeStyle, for: ToolbarPlacement...)

Think of all the work the Swift compiler has to do in calls that use an unqualified first argument:

.toolbarBackground(.hidden, for: .tabBar)
.toolbarBackground(.blue, for: . tabBar)

We often see the Swift compiler as an annoying stickler, but it figures out a lot!

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