I am struggling to write code that allows the user to progressively
select a value from a list. For example from a long list the user
could type R to show all the items starting with R, then type o, to
reduce the list to all items starting with Ro etc.

Secondly if the user types a term that is not on the list, it should
be added to the list for future selection.

As I see it this is the primary purpose of a combo-box but I cant find
the above code. Any help will be appreciated.
Thanks,
Rod