Given a wx:menu% object, items are appended which corresponds to the standard edit commands which can be applied to a buffer with do-edit.
The return value is one greater than the last menu id used by the appended items. (Use this to set the offset for more menu items.)
The id-offset argument offsetd the ids assigned to the menu items (so that they don't collide with menu item ids an application needs to use). If id-offset is zero, pass a selected menu id (sent to on-menu-command or a wx:menu% callback procedure) directly to do-edit; otherwise, subtract the id-offset before calling do-edit.