with a special identifier $-1$ is a separator item and doesn't have an
associated command but just makes a separator line appear in the menu.
+{\bf NB:} Please note that {\it wxID_ABOUT} and {\it wxID_EXIT} are
+predefined by wxWidgets and have a special meaning since entries
+using these IDs will be taken out of the normal menus under MacOS X
+and will be inserted into the system menu (following the appropriate
+MacOS X interface guideline).
+
Menu items may be either normal items, check items or radio items. Normal items
don't have any special properties while the check items have a boolean flag
associated to them and they show a checkmark in the menu when the flag is set.