title: WPF, TextBox.Text bind to TimeSpan type property
body: <p>There is TextBox.Text, which binded to Nullable TimeSpan property. When trying type value to TextBox text input occurs unpredictably.</p>
  
  <p>Code:</p>
  
  <pre><code>&lt;TextBox Grid.Column="0" Grid.Row="0" Width="120" Margin="60,0,0,0" VerticalAlignment="Center" HorizontalAlignment="Left"
                           IsEnabled="{Binding ElementName=ForCv,Path=IsChecked, UpdateSourceTrigger=PropertyChanged}"
                           Text="{Binding Path=TimeFrom, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/&gt;
  </code></pre>
  
  <p>I want to type on mask "00:00:00" but I don`t know how it might work. Mask for this TextBox not defined, it defineds somewhere inside binding or TimeSpan type (for example according ToString() return value method). Please, help.</p>
  
  <p>P.S. Sorry for my eng.</p>