TextField with Custom Binding

I'm just playing with Combine, and I want to limit the number of letters that the text field can show. So I have the following lines of code.

import SwiftUI

struct ContentView: View {
	@State var messageText: String = ""
	
	var body: some View {
		let bindingMessage = Binding {
			messageText
		} set: {
			messageText = String($0.prefix(10))
			print(String($0.prefix(10)))
		}

		Form {
			TextField("Message", text: bindingMessage)
		}
	}
}

I'm expecting that the text field will show only the first 10 letters. But, as the screenshot below indicates, it shows the entire string. What am I doing wrong? Muchos Thankos. It sounds basic. Ugghhh...