This code system http://hl7.org/fhir/codesystem-content-mode defines the following codes:

CodeDisplayDefinition
not-presentNot PresentNone of the concepts defined by the code system are included in the code system resource
exampleExampleA few representative concepts are included in the code system resource
fragmentFragmentA subset of the code system concepts are included in the code system resource
completeCompleteAll the concepts defined by the code system are included in the code system resource