<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>