title: Binding to a sub-property
body: <p>I built a struct named Fraction, with three properties: <em>double Value</em>, <em>int Numerator</em> and <em>int Denominator</em>. In my data source I use the Fraction as a property, <em>Fraction Position</em>.</p>
  
  <p>The data is bound like this:</p>
  
  <pre><code>  &lt;TextBox Text="{Binding Path=Position.Numerator}"/&gt;
    &lt;TextBox Text="{Binding Path=Position.Denominator}"/&gt;
  </code></pre>
  
  <p>but the binding happens to work only one way - from source to target. I tried to catch the SourceUpdated event, but it didn't work.</p>
  
  <p>Is there a way to force two-way binding? I tried <em>Mode=TwoWay</em>, but it didn't work either.</p>