Search parameter for an extension example (id = "example-extension")

<?xml version="1.0" encoding="UTF-8"?>

<SearchParameter xmlns="http://hl7.org/fhir">
  <id value="example-extension"/> 
  <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-wg">
    <valueCode value="fhir"/> 
  </extension> 
  <url value="http://hl7.org/fhir/SearchParameter/example-extension"/> 
  <name value="ExampleSearchParameterOnAnExtension"/> 
  <title value="Example Search Parameter on an extension"/> 
  <status value="draft"/> 
  <experimental value="true"/> 
  <publisher value="HL7 International / FHIR Infrastructure"/> 
  <contact> 
    <telecom> 
      <system value="url"/> 
      <value value="http://www.hl7.org/Special/committees/fiwg"/> 
    </telecom> 
  </contact> 
  <description value="Search by url for a participation agreement, which is stored as an extension referencing
   a DocumentReference"/> 
  <code value="part-agree"/> 
  <base value="Patient"/> 
  <type value="reference"/> 
  <expression value="Patient.extension('http://example.org/fhir/StructureDefinition/participation-agreement').valu
  e"/> 
  <processingMode value="normal"/> 
  <target value="DocumentReference"/> 
</SearchParameter>