Value MUST be part of code list 'Document name code, full list (UNCL1001)' or 'Image code (openPEPPOL)'.
/ubl:Catalogue/cac:CatalogueLine/cac:Item/cac:ItemSpecificationDocumentReference/cbc:DocumentTypeCode
(some $code in $clUNCL1001 satisfies $code = normalize-space(text())) or (some $code in $clImage satisfies $code = normalize-space(text()))