main.swift

import SwiftUI

@main
struct ExampleCommandsApp: App {
    var body: some Scene {
        DocumentGroup(
            newDocument: ExampleCommandsDocument()
        ) { file in
            ContentView(
                document: file.$document
            ).focusedValue(\.document, file.$document)
        }.commands {
            CommandMenu("Document") {
                TestCommand()
            }
        }
    }
}

struct DocumentFocusedValueKey: FocusedValueKey {
    typealias Value = Binding<ExampleCommandsDocument>
}

extension FocusedValues {
    var document: DocumentFocusedValueKey.Value? {
        get {
            return self[DocumentFocusedValueKey.self]
        }
        
        set {
            self[DocumentFocusedValueKey.self] = newValue
        }
    }
}

struct TestCommand: View {
    
    @FocusedBinding(\.document)
    var document: ExampleCommandsDocument?
    
    var body: some View {
        Button("ALL CAPS") {
            document?.text = document?.text.uppercased() ?? ""
        }.disabled(document?.text.uppercased() == document?.text)
    }
}