title: Bind width of UI element to a percentage of another UI element's width
body: <p>Based on <a href="https://stackoverflow.com/questions/5873007/wpf-control-width-binding">this question</a>, but slightly different. </p>
  
  <p>I'm not sure if this is possible. Is there any way to link an UI element's width to another element's width <strong>percentage</strong>? </p>
  
  <p>For example:</p>
  
  <pre><code>&lt;ScrollViewer x:Name="scrollviewerWrapper"&gt;
  
       &lt;TextBlock x:Name="textblock" 
                  Width="{Binding Path=Width, [[[ % of ]]] ElementName=scrollviewerWrapper}" /&gt;
  
  &lt;/ScrollViewer&gt;
  </code></pre>
  
  <p>So if my ScrollViewer is 100px, I want my TextBlock to be 60% of that = 60px (the scrollviewer's width is dynamic). </p>