anchor.diff:  QICoreHelpers.ToConcept(%value.extension[url=http://hl7.org/fhir/us/qicore/StructureDefinition/qicore-doNotPerformReason].value)
   %value.modifierExtension[url=http://hl7.org/fhir/StructureDefinition/request-doNotPerform].value.value
   
  +// TODO: Consider alignment with FHIRPath here? (i.e. use .extension(), rather than this syntax)
  +
   
   // Slicing
   QICoreHelpers.ToConcept(%value.category[coding.system=http://terminology.hl7.org/CodeSystem/observation-category,coding.code=vital-signs].value)
   QICoreHelpers.ToCode(%value.code.coding[system=http://loinc.org,code=39156-5].value)
   %value.component[code.coding.system=http://loinc.org,code.coding.code=8480-6]
   %value.component[code.coding.system=http://loinc.org,code.coding.code=8462-4]
  +
  +// TODO: Consider alignment with FHIRPath here? (i.e. use .where(), rather than this syntax)
  +
  +// TODO: Consider a use case for coalescing? E.g. %value.foo ?? %value.bar ?? %value.baz (using typescript-inspired syntax; is there a FHIRPath variant?). Maybe that's going too far? I mean, I guess we don't want to redefine all of FHIRPath, right?
   */
   
   targetMapping
  
positive.code: %value.value
  QICoreHelpers.ToConcept(%value)
  
  // Choices
  System.DateTime:%value.value;;QICore.Timing:null
  QICore.Reference:null;System.Concept:QICoreHelpers.ToConcept(%value)
  
negative.code: targetIndexItem
    : identifier '=' STRING
    ;
  
  // TODO: Consider use cases for numeric indexes (e.g. component[0] (first item) component[-1] (last item)
  
  mappingTarget
    : '%' identifier
  