struct ComboBox

A closed field showing the current choice, and a dropdown of the rest.

The list is an overlay(alignment: .below), so it paints above everything, escapes any surrounding clip, and takes input before the view underneath — the three things a dropdown needs and a normal child cannot have. Clicking away, or Escape, dismisses it through the same path menus use; nothing here tracks that itself.

@State private var tab = 0
ComboBox(
    selection: $tab,
    items: docs.enumerated().map {
        ComboBoxItem($0.element.name, tag: $0.offset, detail: $0.element.path)
    },
    width: .pt(240)
)

Mouse-driven only: there is no keyboard focus ring or arrow-key navigation yet, because a composed view has no way to hold focus — that belongs to the leaf nodes (TextField, EditorView) and would have to grow a focusable container first.