Response to renegotiate an appointment request

{
  "resourceType" : "AppointmentResponse",
  "id" : "exampleresp",
  "text" : {
    "status" : "generated",
    "div" : "<div xmlns=\"http://www.w3.org/1999/xhtml\">Accept Brian MRI results discussion</div>"
  },
  "identifier" : [{
    "system" : "http://example.org/sampleappointmentresponse-identifier",
    "value" : "response123"
  }],
  "appointment" : {
    "reference" : "Appointment/examplereq",
    "display" : "Brian MRI results discussion"
  },
  "start" : "2013-12-25T13:15:00Z",
  "end" : "2013-12-25T13:30:00Z",
  "participantType" : [{
    "coding" : [{
      "system" : "http://terminology.hl7.org/CodeSystem/v3-ParticipationType",
      "code" : "ATND"
    }]
  }],
  "actor" : {
    "reference" : "Practitioner/example",
    "display" : "Dr Adam Careful"
  },
  "participantStatus" : "tentative",
  "comment" : "can't we try for this time, can't do mornings"
}