Faciliate access to properties of a binding

Sources/Adwaita/Model/Data Flow/Binding.swift

@@ -38,6 +38,7 @@
 /// }
 /// ```
 @propertyWrapper
+@dynamicMemberLookup
 public struct Binding<Value> {
 
     /// The value.
@@ -64,6 +65,17 @@ public struct Binding<Value> {
     /// The closure for settings the value.
     private let setValue: (Value) -> Void
 
+    /// Get a property of any content of a `Binding` as a `Binding`.
+    /// - Parameter dynamicMember: The path to the member.
+    /// - Returns: The binding.
+    public subscript<Subject>(dynamicMember keyPath: WritableKeyPath<Value, Subject>) -> Binding<Subject> {
+        .init {
+            wrappedValue[keyPath: keyPath]
+        } set: { newValue in
+            wrappedValue[keyPath: keyPath] = newValue
+        }
+    }
+
     /// Initialize a property that is bound from a parent view.
     /// - Parameters:
     ///   - get: The closure for getting the value.

user-manual/Basics/CreatingViews.md

@@ -131,6 +131,13 @@ struct ChangeTextView: View {
 }
 ```
 
+If you have a more complex type and want to pass a property of the type as a binding,
+you can just access the property on the binding.
+
+```swift
+HelloView(text: $complexType.text)
+```
+
 Whenever you modify a state property (directly or indirectly through bindings),
 the user interface gets automatically updated to reflect that change.