I am trying to format a column so that it keeps track of
computer hardware mac addresses.

-Each cell must be limited to 17 characters only.
-Cells must have 5 visible permanent colons so that users
may only enter the remaining 12 letters/numbers.
-cells must be restricted to entry of letters and numbers
(no special characters).
-users must be presented with an error message if they try
to leave the cell without entering 12 letters/numbers.
-column must not accept duplicate mac addresses.


Can anyone give me some direction on how to do this?

Adrian
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