anchor.diff:  targetIndexItem
     : identifier '=' STRING
     ;
  +
  +// TODO: Consider use cases for numeric indexes (e.g. component[0] (first item) component[-1] (last item)
   
   mappingTarget
     : '%' identifier
  
positive.code: 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
  
  
  // 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]
  */
  
  targetMapping
  
negative.code: %value.value
  QICoreHelpers.ToConcept(%value)
  
  // TODO: Consider alignment with FHIRPath here, $value could be $this?
  // The challenge is that %value is more of a replacement token, and are some FHIR maps that will already have $this (slicing maps in particular often include $this)
  
  // Choices
  System.DateTime:%value.value;;QICore.Timing:null
  QICore.Reference:null;System.Concept:QICoreHelpers.ToConcept(%value)
  