Menu enabling and "_documentWindow"

FROM : Sanford Selznick
DATE : Sun Jun 04 05:58:31 2006

I'm having an odd problem.  I have an NSDocument application.  In my
MainMenu.nib I've added an action for a menu item.  I handle this
selector in the MyDocument instance.  The menu item enables and
disables perfectly.  (Go Cocoa!)

However, I want the same menu item to be available in a particular
sheet that I sometimes open on document windows.  So I added the same
selector to the sheet's NSWindowController subclass.

Now, whenever I roll over the menu containing the menu item, I get:

-[MyNSWindowController _documentWindow]: selector not recognized...

Any ideas why simply adding the selector to the NSWindowController
subclass is causing this problem?  What's _documentWindow?  And why's
it not recognized?

Is there some trick with enabling menu items with sheets open?

Thank you,
  Sanford

PS - I'm creating the sheet with [NSApp beginSheet...