Document format as per Annex 3 EPRO-FDHA, Chapter 2.5.
This unambiguous code defines the format of the XDS document. Together with the mimetype,
this should provide the potential consumer with sufficient information as to whether
they are in a position to process the document.
Legenda: Type L=leaf, S=specializable, A=abstract, D=deprecated. NullFlavors to appear
in @nullFlavor attribute instead of @code. NullFlavor OTH (other) suggests text in
originalText.