Makes the object item a member item of the circular queue, inserting the item at the end of the circular queue.

If the circular queue is full, then the first item will be deleted, before the insertion takes place. In this case the deleted item will be returned, otherwise .nil will be returned.

If option is specified, it may be "Normal" or "Unique". The default is "Normal". Only the capitalized letter is needed; all characters following it are ignored. If option is 'Unique', any matching items already in the queue will be removed before item is added to the queue. This allows you to maintain a list like the recent files list of an editor.