Form2.xaml

<UserControl x:Class="Elmish.WPF.Samples.SubModelOpt.Form2"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:vm="clr-namespace:Elmish.WPF.Samples.SubModelOpt;assembly=SubModelOpt.Core"
             Padding="10"
             mc:Ignorable="d"
             d:DataContext="{x:Static vm:Program.form2DesignVm}">
  <StackPanel Width="300">
    <TextBlock Text="Form 2" FontSize="18" FontWeight="Bold" HorizontalAlignment="Center" Margin="0,0,0,5" />
    <TextBox Text="{Binding Text1, UpdateSourceTrigger=PropertyChanged}" Margin="0,5,0,5" />
    <TextBox Text="{Binding Text2, UpdateSourceTrigger=PropertyChanged}" Margin="0,5,0,5" />
    <Button Command="{Binding Submit}" Content="Submit" />
  </StackPanel>
</UserControl>