authority 

In case of an external reference the attribute authority defines the issuing authority of the unique identifier for the external classification, which is given in the attribute uid.

Attribute Information

Used By

Attribute Group attlist.Reference

Source 

<xs:attribute name="authority" type="xs:NMTOKEN">
  <xs:annotation>
    <xs:documentation xml:lang="en-US">In case of an external reference the attribute authority defines the issuing authority of the unique identifier for the external classification, which is given in the attribute uid.</xs:documentation>
  </xs:annotation>
</xs:attribute>

Sample