How to send actions across nibs ?

I have a document-based app and I want certain menu items (in MainMenu.nib) to send actions to the front document (and likewise be disabled when there is no document to send actions to)…
In MainMenu.nib, make a connection from your menu item to the nib's FirstResponder action you desire.
If the action you want to connect is not already defined by Cocoa, you have to add it to the list of available ones:
In the nib window, select the FirstResponder icon in the Instances tab view, then select the Classes tab view and display the Info window (command shift I), select the Actions tab and eventually add you new action(s).