This is the CodeSystem that contains all the codes in DDCC Composition Category Codes (http://smart.who.int/ddcc/CodeSystem/DDCCCompositionCategoryCodeSystem) and DDCC Composition Category Codes (http://smart.who.int/ddcc/CodeSystem/DDCCCompositionCategoryCodeSystem). E.g. what you have to deal with if you get resources containing codes in either of them