Existing Wording
data missing code

Comments
This seems like "nullFlavors" in HL7 but the values listed for FHIR (unknown | asked | temp | notasked | masked | unsupported | astext | error" are not given definitions. Even though several seem equivalent to nullFlavors like UNK, ASKU, etc., it's hard to be sure, or to know the reason for differences. I suggest using the existing nullFlavors. I realize that nullFlavors are not perfect and may change, but at least both FHIR and CDA could point to the same definitions that ought to be used across all HL7, since these are semantics, not technical issues. As with negation, "unknown data" is an important and much-discussed topic of the past few years, and a challenge for implementers, so FHIR should strive to be very clear and have its definitions in place.

Grahame's Comments
MnM to review; this couldresolved by mapping to mullFlavors, by revising the nullFalvors, or by falling back to the nullFlavors. However there are few codes here - http://hl7.org/implement/standards/FHIR-Develop/data-absent-reason.html - that are missing in the nullFlavors. btw, then link given above does have definitions (maybe reduce the link depth here_