This code system http://hl7.org/fhir/action-relationship-type defines the following codes:

Code Display Definition
before-start Before Start The action must be performed before the start of the related action.
before Before The action must be performed before the related action.
before-end Before End The action must be performed before the end of the related action.
concurrent-with-start Concurrent With Start The action must be performed concurrent with the start of the related action.
concurrent Concurrent The action must be performed concurrent with the related action.
concurrent-with-end Concurrent With End The action must be performed concurrent with the end of the related action.
after-start After Start The action must be performed after the start of the related action.
after After The action must be performed after the related action.
after-end After End The action must be performed after the end of the related action.
<status value="draft"/><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="Defines the types of relationships between actions."/><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/action-relationship-type"/><content value="complete"/><concept><code value="before-start"/><display value="Before Start"/><definition value="The action must be performed before the start of the related action."/></concept><concept><code value="before"/><display value="Before"/><definition value="The action must be performed before the related action."/></concept><concept><code value="before-end"/><display value="Before End"/><definition value="The action must be performed before the end of the related action."/></concept><concept><code value="concurrent-with-start"/><display value="Concurrent With Start"/><definition value="The action must be performed concurrent with the start of the related action."/></concept><concept><code value="concurrent"/><display value="Concurrent"/><definition value="The action must be performed concurrent with the related action."/></concept><concept><code value="concurrent-with-end"/><display value="Concurrent With End"/><definition value="The action must be performed concurrent with the end of the related action."/></concept><concept><code value="after-start"/><display value="After Start"/><definition value="The action must be performed after the start of the related action."/></concept><concept><code value="after"/><display value="After"/><definition value="The action must be performed after the related action."/></concept><concept><code value="after-end"/><display value="After End"/><definition value="The action must be performed after the end of the related action."/></concept></CodeSystem>