By default, CAPI dialogs on Cocoa use sheets which are application-modal. This means that the application waits until the sheet is dismissed and does not allow the user to work with its other windows until then.
This section describes how to create CAPI dialogs which are window-modal on Cocoa. This is done with portable code, so Windows, GTK+ and Motif programmers may wish to code their CAPI dialogs as described in this section, which would ease a future port to the Cocoa GUI.
CAPI User Guide (Unix version) - 30 Aug 2011