Imports System
Imports Microsoft.Windows.Design.Model
Imports Microsoft.Windows.Design.Features

<Feature(GetType(ButtonDefaults))>  _
Public Class DemoButton
End Class

Class ButtonDefaults
    Inherits DefaultInitializer

    Public Overrides Sub InitializeDefaults(ByVal item As ModelItem) 
        item.Content.SetValue("Button")

    End Sub
End Class

using System;

using Microsoft.Windows.Design.Model;
using Microsoft.Windows.Design.Features;

namespace DemoControlLibrary.VisualStudio.Design
{
    [Feature(typeof(ButtonDefaults))]
    public class DemoButton { }

    class ButtonDefaults : DefaultInitializer
    {
        public override void InitializeDefaults(ModelItem item)
        {
            item.Content.SetValue("Button");
        }
    }
}