Formal Definition for _filter parameter (id = "filter")

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

<SearchParameter xmlns="http://hl7.org/fhir">
  <id value="filter"/> 
  <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-wg">
    <valueCode value="fhir"/> 
  </extension> 
  <url value="http://hl7.org/fhir/SearchParameter/filter"/> 
  <version value="1"/> 
  <name value="FilterSearchParameter"/> 
  <title value="Filter Search Parameter"/> 
  <status value="draft"/> 
  <experimental value="false"/> 
  <date value="2018-07-26"/> 
  <publisher value="HL7 International / FHIR Infrastructure"/> 
  <contact> 
    <telecom> 
      <system value="url"/> 
      <value value="http://www.hl7.org/Special/committees/fiwg"/> 
    </telecom> 
  </contact> 
  <description value="This is the formal declaration for the _filter parameter, documented at [http://hl7.org/fhir/
  search_filter.html](http://hl7.org/fhir/search_filter.html)"/> 
  <purpose value="Support combination searches when the simple name=value basis of search cannot
   express what is required"/> 
  <code value="_filter"/> 
  <base value="Resource"/> 
  <type value="special"/> 
</SearchParameter>