The \xmlelement{sendstatus} indication has the values 'true' or 'false'.
It indicates whether the sender would like to receive is-composing
indications.

    <xs:simpleType name="sendstatus">
      <xs:restriction base="xs:string">
        <xs:enumeration value="true"/>
        <xs:enumeration value="false"/>
      </xs:restriction>
    </xs:simpleType>