This is a multivalued attribute whose values consist of a 5 tuple: (attribute name), (column title), (default visibility (0,1)), (column width ( 1 for auto width)), 0 (reserved for future use must be zero). This value is used by the AD Users and Computers console.
Entry
Value
CN
Extra-Columns
Ldap-Display-Name
extraColumns
Size
Each value would be the size of the string of the 5 tuple above. By default there will be 22 values on the default-Display object in the DisplaySpecifier container.
Update Privilege
Domain administrator
Update Frequency
This will only be updated if a service like Exchange is installed.