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

Code Display Definition
deny-overrides Deny-overrides The deny overrides combining algorithm is intended for those cases where a deny decision should have priority over a permit decision.
permit-overrides Permit-overrides The permit overrides combining algorithm is intended for those cases where a permit decision should have priority over a deny decision.
ordered-deny-overrides Ordered-deny-overrides The behavior of this algorithm is identical to that of the “Deny-overrides” rule-combining algorithm with one exception. The order in which the collection of rules is evaluated SHALL match the order as listed in the permission.
ordered-permit-overrides Ordered-permit-overrides The behavior of this algorithm is identical to that of the “Permit-overrides” rule-combining algorithm with one exception. The order in which the collection of rules is evaluated SHALL match the order as listed in the permission.
deny-unless-permit Deny-unless-permit The “Deny-unless-permit” combining algorithm is intended for those cases where a permit decision should have priority over a deny decision, and an “Indeterminate” or “NotApplicable” must never be the result. It is particularly useful at the top level in a policy structure to ensure that a PDP will always return a definite “Permit” or “Deny” result.
permit-unless-deny Permit-unless-deny The “Permit-unless-deny” combining algorithm is intended for those cases where a deny decision should have priority over a permit decision, and an “Indeterminate” or “NotApplicable” must never be the result. It is particularly useful at the top level in a policy structure to ensure that a PDP will always return a definite “Permit” or “Deny” result. This algorithm has the following behavior.
<status value="active"/> <experimental value="false"/> <date value="2022-08-05T10:01:24+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="Codes identifying the rule combining. See XACML Combining algorithms http://docs.oasis-open.org/xacml/3.0/xacml-3.0-core-spec-cos01-en.html"/> <jurisdiction> <coding> <system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/> <code value="001"/> <display value="World"/> </coding> </jurisdiction> <caseSensitive value="true"/> <content value="complete"/> <concept> <code value="deny-overrides"/> <display value="Deny-overrides"/> <definition value="The deny overrides combining algorithm is intended for those cases where a deny decision should have priority over a permit decision."/> </concept> <concept> <code value="permit-overrides"/> <display value="Permit-overrides"/> <definition value="The permit overrides combining algorithm is intended for those cases where a permit decision should have priority over a deny decision."/> </concept> <concept> <code value="ordered-deny-overrides"/> <display value="Ordered-deny-overrides"/> <definition value="The behavior of this algorithm is identical to that of the “Deny-overrides” rule-combining algorithm with one exception. The order in which the collection of rules is evaluated SHALL match the order as listed in the permission."/> </concept> <concept> <code value="ordered-permit-overrides"/> <display value="Ordered-permit-overrides"/> <definition value="The behavior of this algorithm is identical to that of the “Permit-overrides” rule-combining algorithm with one exception. The order in which the collection of rules is evaluated SHALL match the order as listed in the permission."/> </concept> <concept> <code value="deny-unless-permit"/> <display value="Deny-unless-permit"/> <definition value="The “Deny-unless-permit” combining algorithm is intended for those cases where a permit decision should have priority over a deny decision, and an “Indeterminate” or “NotApplicable” must never be the result. It is particularly useful at the top level in a policy structure to ensure that a PDP will always return a definite “Permit” or “Deny” result."/> </concept> <concept> <code value="permit-unless-deny"/> <display value="Permit-unless-deny"/> <definition value="The “Permit-unless-deny” combining algorithm is intended for those cases where a deny decision should have priority over a permit decision, and an “Indeterminate” or “NotApplicable” must never be the result. It is particularly useful at the top level in a policy structure to ensure that a PDP will always return a definite “Permit” or “Deny” result. This algorithm has the following behavior."/> </concept> </CodeSystem>