{

"resourceType": "SearchParameter",
"id": "example-extension",
"url": "http://hl7.org/fhir/SearchParameter/example-extension",
"name": "Example Search Parameter on an extension",
"status": "draft",
"experimental": true,
"publisher": "Health Level Seven International (FHIR Infrastructure)",
"contact": [
  {
    "telecom": [
      {
        "system": "url",
        "value": "http://hl7.org/fhir"
      }
    ]
  }
],
"description": "Search by url for a participation agreement, which is stored in a DocumentReference",
"code": "part-agree",
"base": [
  "Patient"
],
"type": "reference",
"expression": "DocumentReference.extension('http://example.org/fhir/StructureDefinition/participation-agreement')",
"xpath": "f:DocumentReference/f:extension[@url='http://example.org/fhir/StructureDefinition/participation-agreement']",
"xpathUsage": "normal",
"target": [
  "DocumentReference"
]

}