Jabber
From:  http://docs.jabber.org/draft-miller-impp-jabber-00.html

Appendix B. XML Streams DTD

<!ELEMENT stream (error?)>
<!ATTLIST stream
  to              CDATA       #REQUIRED
  from            CDATA       #IMPLIED
  id              CDATA       #IMPLIED
  xmlns           CDATA       #REQUIRED
  xmlns:stream    CDATA       #REQUIRED 'http://etherx.jabber.org/streams'
  >
<!ELEMENT error (PCDATA)>