static void ValueChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            CompositeTextBox me = d as CompositeTextBox;

            if (me != null && e != null && e.NewValue != null)
            {
                me.Parameter = new ViewModel.Funcs.FuncParameter(me.Header, e.NewValue.ToString());
            }
        }
        static void ParameterChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            CompositeTextBox me = d as CompositeTextBox;

            if (me != null && e != null && e.NewValue != null)
            {
                ViewModel.Funcs.FuncParameter newValue = (ViewModel.Funcs.FuncParameter)e.NewValue;
                me.Header = newValue.Name;
                me.SetValue(ValueProperty, newValue.Value);
            }
        }