title: Two way percentage formatted binding in WPF
body: <p>I have this textbox:</p>
  
  <pre><code>&lt;TextBox Text="{Binding Path=TaxFactor, StringFormat=P}" /&gt;
  </code></pre>
  
  <p>It correctly displays <code>0.05</code> as <code>5%</code>, but it doesn't work going back. When I type in a percentage, it fails because of the percent symbol. If I try writing just a number, like <code>5</code>, I get <code>500%</code> instead. I have to write <code>0.05</code> for it to work.</p>
  
  <p>Do I have to write a custom converter to get my percentage back? And if so, how do I get around locale-specific percentage formats?</p>