url

<xs:attribute name="url">
  <xs:annotation>
    <xs:documentation>The attribute url contains the url where one can find the source.</xs:documentation>
  </xs:annotation>
  <xs:simpleType>
    <xs:restriction base="xs:anyURI">
      <xs:minLength value="1"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>