This code system http://hl7.org/fhir/http-operations defines the following codes:

CodeDisplayDefinition
delete DELETEHTTP DELETE operation.
get GETHTTP GET operation.
options OPTIONSHTTP OPTIONS operation.
patch PATCHHTTP PATCH operation.
post POSTHTTP POST operation.
put PUTHTTP PUT operation.
head HEADHTTP HEAD operation.
<status value="active"/><experimental value="false"/><date value="2021-01-05T10:01:24+11:00"/><publisher value="HL7 (FHIR Project)"/><contact><telecom><system value="url"/><value value="http://hl7.org/fhir"/></telecom><telecom><system value="email"/><value value="fhir@lists.hl7.org"/></telecom></contact><description value="The allowable request method or HTTP operation codes."/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/http-operations"/><content value="complete"/><concept><code value="delete"/><display value="DELETE"/><definition value="HTTP DELETE operation."/></concept><concept><code value="get"/><display value="GET"/><definition value="HTTP GET operation."/></concept><concept><code value="options"/><display value="OPTIONS"/><definition value="HTTP OPTIONS operation."/></concept><concept><code value="patch"/><display value="PATCH"/><definition value="HTTP PATCH operation."/></concept><concept><code value="post"/><display value="POST"/><definition value="HTTP POST operation."/></concept><concept><code value="put"/><display value="PUT"/><definition value="HTTP PUT operation."/></concept><concept><code value="head"/><display value="HEAD"/><definition value="HTTP HEAD operation."/></concept></CodeSystem>