cap:onset

<element name="onset" minOccurs="0">
  <simpleType>
    <restriction base="xs:dateTime">
      <pattern value="\d\d\d\d-\d\d-\d\dT\d\d:\d\d:\d\d[-,+]\d\d:\d\d"/>
    </restriction>
  </simpleType>
</element>