2c389a02__Specifications___openEHR_wiki__openEHR_equivalent
[0] 2 [Code mnemonic] UNK [Rubric] unknown [Description] A proper value is applicable, but not known. [openEHR equivalent] 
(same in openEHR)
Null Flavours and Boolean data in openEHR - Specifications - openEHR wiki
openEHR equivalent