This code system http://hl7.org/fhir/graph-compartment-rule defines the following codes:

CodeDisplayDefinition
identical IdenticalThe compartment must be identical (the same literal reference).
matching MatchingThe compartment must be the same - the record must be about the same patient, but the reference may be different.
different DifferentThe compartment must be different.
custom CustomThe compartment rule is defined in the accompanying FHIRPath expression.
<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="How a compartment must be linked."/><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/graph-compartment-rule"/><content value="complete"/><concept><code value="identical"/><display value="Identical"/><definition value="The compartment must be identical (the same literal reference)."/></concept><concept><code value="matching"/><display value="Matching"/><definition value="The compartment must be the same - the record must be about the same patient, but the reference may be different."/></concept><concept><code value="different"/><display value="Different"/><definition value="The compartment must be different."/></concept><concept><code value="custom"/><display value="Custom"/><definition value="The compartment rule is defined in the accompanying FHIRPath expression."/></concept></CodeSystem>