title: Show contextual menu on ctrl-click/right-click on header of NSTableView
body: <p>I'm searching for an elegant way to detect a right-click/ctrl-click on the header of an NSTableView.</p>
  
  <p>When the right click occurs, I want to display an contextual menu.</p>
  
  <pre><code>- (NSMenu *)menuForEvent:(NSEvent *)
  </code></pre>
  
  <p>detects only right clicks in the table - not in the header of the table.</p>
  
  <p>thanks for your help.</p>