t :: %HL7.Segment.MSH{__segment__: term, accept_ack_type: binary, app_ack_type: binary, char_set: binary, continuation_pointer: binary, country_code: binary, encoding_chars: binary, field_separator: binary, message_control_id: binary, message_datetime: :calendar.datetime, message_type: HL7.Composite.CM_MSH_9.t, processing_id: binary, receiving_app: HL7.Composite.HD.t, receiving_facility: HL7.Composite.HD.t, security: binary, sending_app: HL7.Composite.HD.t, sending_facility: HL7.Composite.HD.t, sequence_number: integer, version: binary}