Inserts an item into the list at the specified position.
You can insert a Bookmark directly or you can use one of the
overloaded operators to insert a bookmark with a specified
When you insert a string this is encapsulated within a new
Bookmark which is then inserted.
Bookmarks can exist in only one place at a time. If the Bookmark
supplied is already contained by another object then a Clone of the
Bookmark is added.
If the index equals the number of items in the array then the
bookmark is appended to the end.
If the index is not a valid index this method throws an