This case-sensitive code system http://www.whocc.no/atc defines codes, but no codes are represented here

 <status value="active"/> <experimental value="false"/> <date value="2019-03-20T00:00:00-04:00"/> <publisher value="TBD - External Body"/> <contact> <name value="World Health Organization"/> </contact> <description value="WHO ATC"/> <caseSensitive value="true"/> <content value="not-present"/> </CodeSystem>