title: Reusing property editors for Blend 4
body: <p>I have a custom silverlight control, which exposes a property with DataGridLength type. Now I want  that property to have the same editor as a common DataGridColumn's Width property, with the combobox and everything, like this:<br>
   <img src="https://i.stack.imgur.com/2tkgI.png" alt="enter image description here"><br>
  instead, I only get a simple TextBox, with "Auto" written in, with no way to set to SizeToCells and so on.<br>
  I assume I need a DesignTime attribute, but none of the ones I found in ComponentModel namespace even came close...</p>