The definition currently says " This value set includes codes from BCP-47. This value set matches the ONC 2015 Edition LanguageCommunication data element value set within C-CDA to use a 2 character language code if one exists, and a 3 character code if a 2 character code does not exist. It points back to RFC 5646, however only the language codes are required, all other elements are optional."

The definition, even combined with the LCD, doesn't really provide the user with any definitive information as to how to construct this value set. Instead, one could look further in RFC 5646 and end up at this USCDI page: https://www.healthit.gov/isa/representing-patient-preferred-language-presently

Following that bread crumb to the Applicable Value Set...would lead the implementer to a value set that only includes three character codes (therefore not following the guidance to use only 2 character codes if they exist).

Instead, I'd propose that the definition be updated to explicitly say the value set is composed of ISO 639-1 and ISO 639-2 where the two character should be used if present etc...

Existing Wording:

LCD currently reads - "Include codes from urn:ietf:bcp:47 where ext-lang doesn't exist, script doesn't exist, variant doesn't exist, extension doesn't exist and private-use doesn't exist"

Proposed Wording:

"Includes code from urn:ietf:bcp:47 represented as the union of 639-1 and 639-2 where code from 639-1 should be used if present, where ext-lang doesn't exist, script doesn't exist, variant doesn't exist, extension doesn't exist and private-use doesn't exist"

(Comment 13 - imported by: Jean Duteau)