@type t() :: %ICal.Event{
  alarms: [ICal.Alarm.t()],
  attachments: [ICal.Attachment.t()],
  attendees: [String.t()],
  categories: [String.t()],
  class: String.t() | nil,
  comments: [String.t()],
  contacts: [ICal.Contact.t()],
  created: ICal.optional_rfc5455_datetime(),
  custom_properties: ICal.custom_properties(),
  description: String.t() | nil,
  dtend: ICal.optional_rfc5455_date(),
  dtstamp: ICal.optional_rfc5455_datetime(),
  dtstart: ICal.optional_rfc5455_date(),
  duration: ICal.Duration.t() | nil,
  exdates: [Date.t() | ICal.rfc5455_datetime()],
  geo: ICal.geo() | nil,
  location: String.t() | nil,
  modified: ICal.optional_rfc5455_date(),
  organizer: String.t() | nil,
  priority: integer() | nil,
  rdates: [Date.t() | ICal.rfc5455_datetime() | ICal.period()],
  recurrence_id: ICal.optional_rfc5455_date(),
  related_to: [String.t()],
  request_status: [ICal.RequestStatus.t()],
  resources: [String.t()],
  rrule: ICal.Recurrence.t() | nil,
  sequence: String.t() | nil,
  status: :tentative | :confirmed | :cancelled | nil,
  summary: String.t() | nil,
  transparency: :opaque | :transparent | nil,
  uid: String.t() | nil,
  url: String.t() | nil
}