title: Cleanest way to bind a Button's visibility to the contents of two textboxes
body: <p>I have a <code>Button</code> within my app whose "enabledness" I have bound to whether a <code>TextBox</code> is empty as so:</p>
  
  <pre><code>&lt;Button Content="Go" 
          IsEnabled="{Binding Text, 
                      Converter={StaticResource EnableIfStringNotEmptyDataSource}, 
                      ElementName=MyTextbox}"/&gt;
  </code></pre>
  
  <p>(implementation of <code>EnableIfStringNotEmptyDataSource</code> omitted for brevity).</p>
  
  <p>This automatically changes the state when the <code>TextBox</code>'s text changes.</p>
  
  <p>What would be the most elegant way of binding a property in the same manner to whether <strong>two</strong> textboxes are both empty or not?</p>