A typical message definition

{
  "resourceType" : "MessageDefinition",
  "id" : "example",
  "text" : {
    "status" : "generated",
    "div" : "<div xmlns=\"http://www.w3.org/1999/xhtml\">Message definition base example</div>"
  },
  "extension" : [{
    "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-wg",
    "valueCode" : "inm"
  }],
  "url" : "http://hl7.org/fhir/MessageDefinition/example",
  "identifier" : [{
    "system" : "urn:ietf:rfc:3986",
    "value" : "urn:oid:2.16.840.1.113883.4.642.15.3"
  }],
  "name" : "EXAMPLE",
  "title" : "Message definition base example",
  "status" : "draft",
  "experimental" : true,
  "date" : "2016-11-09",
  "publisher" : "HL7 International / Infrastructure And Messaging",
  "contact" : [{
    "telecom" : [{
      "system" : "url",
      "value" : "http://www.hl7.org/Special/committees/inm"
    }]
  }],
  "description" : "Message definition base example",
  "purpose" : "Defines a base example for other MessageDefinition instances.",
  "eventCoding" : {
    "system" : "http://example.org/fhir/message-events",
    "code" : "admin-notify"
  },
  "category" : "notification"
}