如何向标准XAML元素添加其他属性？

public class CustomProperty : DependencyProperty
{
    public static readonly DependencyProperty CustomPropertyProperty =
        DependencyProperty.RegisterAttached("CustomProperty", typeof(string), typeof(CustomProperty), new PropertyMetadata(null));

    public static string GetCustomProperty(DependencyObject obj)
    {
        return (string)obj.GetValue(CustomPropertyProperty);
    }

    public static void SetCustomProperty(DependencyObject obj, string value)
    {
        obj.SetValue(CustomPropertyProperty, value);
    }
}