A code set is a special data type that consists of a list of predefined value pairs,
"Code" and "Description", that contain all possible values for the attribute. When the
attribute is displayed for editing by the user, the user will be presented with the list of
paired values to choose from. If the Code and Description values are the same, only the Code
will be displayed. If the Code and Description are different, they will be displayed as
<Code Value> -- <Description Value>".