This code system http://terminology.hl7.org/CodeSystem/communication-category defines the following codes:

CodeDisplayDefinition
alert AlertThe communication conveys an alert.
notification NotificationThe communication conveys a notification.
reminder ReminderThe communication conveys a reminder.
instruction InstructionThe communication conveys an instruction.
 <status value="draft"/> <experimental value="false"/> <date value="2020-04-09T21:10:28+00:00"/> <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 for general categories of communications such as alerts, instructions, etc."/> <caseSensitive value="true"/> <valueSet value="http://terminology.hl7.org/ValueSet/communication-category"/> <content value="complete"/> <concept> <code value="alert"/> <display value="Alert"/> <definition value="The communication conveys an alert."/> </concept> <concept> <code value="notification"/> <display value="Notification"/> <definition value="The communication conveys a notification."/> </concept> <concept> <code value="reminder"/> <display value="Reminder"/> <definition value="The communication conveys a reminder."/> </concept> <concept> <code value="instruction"/> <display value="Instruction"/> <definition value="The communication conveys an instruction."/> </concept> </CodeSystem>