Dependency Property on WPF Custom Control Library

WindowsCaption.xaml.cs

public static readonly DependencyProperty CaptionTextProperty = DependencyProperty.Register(
	"CaptionText",
	typeof(string),
	typeof(WindowCaption),
	new UIPropertyMetadata(CaptionTextChanged));

public static void CaptionTextChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
    ((WindowCaption)(sender)).Caption = e.NewValue.ToString();
}

private string Caption
{
    get
    {
        return tbWindowCaption.Text;
    }
    set
    {
        tbWindowCaption.Text = value;
    }
}
public string CaptionText
{
    get
    {
        return (string)this.GetValue(CaptionTextProperty);
    }
    set
    {
        this.SetValue(CaptionTextProperty, value);
    }
}