{
  "resourceType": "StructureDefinition",
  "meta": {
    "lastUpdated": "2018-10-24T12:04:04.97+00:00"
  },
  "url": "http://example.org/fhir/StructureDefinition/MyExtension",
  "name": "Spoken language",
  "status": "draft",
  "date": "2018-10-24T12:04:05.0890362+00:00",
  "fhirVersion": "3.0.1",
  "kind": "complex-type",
  "abstract": false,
  "contextType": "resource",
  "context": [
    "Patient.communication.preferred"
  ],
  "type": "Extension",
  "baseDefinition": "http://hl7.org/fhir/StructureDefinition/Extension",
  "derivation": "constraint",
  "differential": {
    "element": [
      {
        "id": "Extension",
        "path": "Extension",
        "short": "Test",
        "definition": "Optional Extension Element - found in all resources.",
        "constraint": [
          {
            "key": "ext-1",
            "severity": "error",
            "human": "Must have either extensions or value[x], not both",
            "expression": "extension.exists() != value.exists()",
            "xpath": "exists(f:extension)!=exists(f:*[starts-with(local-name(.), 'value')])"
          }
        ],
        "mapping": [
          {
            "identity": "rim",
            "map": "N/A"
          }
        ]
      },
      {
        "id": "Extension.url",
        "path": "Extension.url",
        "fixedUri": "http://example.org/fhir/StructureDefinition/MyExtension"
      }
    ]
  }
}