This is the ValueSet that contains all the codes in IHE MHD Identifier Types ValueSet (https://profiles.ihe.net/ITI/MHD/ValueSet/IHE.MHD.MHDIdentifierTypeVS) and IHE MHD Identifier Types ValueSet (https://profiles.ihe.net/ITI/MHD/ValueSet/IHE.MHD.MHDIdentifierTypeVS). E.g. what you have to deal with if you get resources containing codes in either of them