title: How to register an Visual Studio extender provider for a document
body: <p>I need to add a property to the property grid of each project item. However, if I register my extender provider with <code>EnvDTE.Constants.vsCATIDDocument</code>, it is never called. It works if I register it with <code>vsCATIDSolutionBrowseObject</code>, but it's not what I want...</p>
  
  <p>I register the extender provider in the <code>Initialize</code> method of my package:</p>
  
  <pre><code>var dte = (DTE) GetGlobalService(typeof(DTE));
  _extenderProvider = new TheExtenderProvider();
  _extenderProviderCookie = dte.ObjectExtenders.RegisterExtenderProvider(EnvDTE.Constants.vsCATIDDocument, "TheExtenderProvider", _extenderProvider);
  </code></pre>
  
  <p>How can I make it work? Should I use a different CATID ?</p>