<StructureDefinition xmlns="http://hl7.org/fhir">
  <url value="https://example.org/fhir/StructureDefinition/MyPatient" />
  <name value="MyPatient" />
  <status value="draft" />
  <fhirVersion value="4.0.1" />
  <kind value="resource" />
  <abstract value="false" />
  <type value="Patient" />
  <baseDefinition value="http://hl7.org/fhir/StructureDefinition/Patient" />
  <derivation value="constraint" />
  <differential>
    <element id="Patient">
      <path value="Patient" />
      <condition value="patient.birthDate" />
      <constraint>
        <key value="patient-birthdate-regex" />
        <severity value="error" />
        <human value="Ensure patient.birthDate is a valid date within a specified range" />
        <expression value="birthDate &gt;= @1900-01-01 and birthDate &lt; today() and birthDate.toString().matches('^(19|20)\\d\\d-(0[1-9]|1[0-2])-(0[1-9]|[12]\\d|3[01])$')" />
      </constraint>
    </element>
    <element id="Patient.identifier">
      <path value="Patient.identifier" />
      <min value="1" />
    </element>
    <element id="Patient.gender">
      <path value="Patient.gender" />
      <fixedCode value="Male" />
    </element>
  </differential>
</StructureDefinition>