Property extension : WideString; (Read/Write)
A character string as a unique identifier within the scope of the identifier root.
The root and extension scheme means that the concatenation of root and extension SHALL be a globally unique identifier for the item that this II value identifies.
Some identifier schemes define certain style options to their code values. For example, the U.S. Social Security Number (SSN) is normally written with dashes that group the digits into a pattern "123-12-1234". However, the dashes are not meaningful and a SSN can also be represented as "123121234" without the dashes. In the case where identifier schemes provide for multiple representations, HL7 or ISO may make a ruling about which is the preferred form and document that ruling where that respective external identifier scheme is recognized.
If no extension attribute is provided in a non-null II, then the root is the complete unique identifier. If the root is not a complete unique identifier, and the extension is not known, then the II SHALL have a nullFlavor even if the root is populated.