<p>Say I have a user control like the one below, how would I bind something to the <code>ActualWidth</code> of the "G1" grid from outside of the control?</p>

<pre><code>&lt;UserControl x:Class="Blah"&gt;
  &lt;WrapPanel&gt;
    &lt;Grid x:Name="G1"&gt;
      ...
    &lt;/Grid&gt;
    &lt;Grid&gt;
      ...
    &lt;/Grid&gt;
  &lt;/WrapPanel&gt;
&lt;/UserControl&gt;
</code></pre>

If you want to bind to an external control where you use this user control, declare a
```
DependencyProperty
```
at your UserControl code behind and then Bind G1 to that property.
And bind the external control's property to the UserControl's
```
DependencyProperty
```
. 
It is like a 2 level of indirection.