Path
     Range.high.Quantity.code
     Id
     Quantity.code
     Type
    
     Cardinality
     0 - 1
     Definition
     A computer processable form of the unit in some unit representation system.
     Comment
     The preferred system is UCUM, but SNOMED CT can also be used (for customary units) or ISO 4217 for currency.  The context of use may additionally require a code from a particular system.
    
     Requirements
     Need a computable form of the unit that is fixed across all forms. UCUM provides this for quantities, but SNOMED CT provides many units of interest.
    
    
    
     Constraint
     
      
      
      All FHIR elements must have a @value or children