Preferred number in ISO II datatype

I was asking myself the question of how to indicate a preferred number (NL:voorkeursnummer) for de id values of a Patient. And of course there is an answer for that:

"II.displayable: Specifies if the identifier is intended for human display and data entry (displayable = true) as opposed to pure machine interoperation (displayable = false)."

-- Source: HL7 Implementation Guidance for Unique Object Identifiers (OIDs), Release 1

NHS Connecting for Health: NHS of the future

Great video about how we (IT) can help making healthcare better.