<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>