DOCBOOK-APPS: Bug in DocBook backends?

[Bernd Kreimeier <bk@lokigames.com>]

The elements below do not trigger any parser error, and 
seem legitimate (w.o printhistory and para they do get
rejected), but there is no output generated.

                                         b.

  <bookinfo>
    ... 

    <printhistory>
    <para>
    <revhistory>

    <revision>
    <revnumber>1.2</revnumber>
    <date>8 March 2000</date>
    <authorinitials>mkv</authorinitials>
    <revremark>blah</revremark>  
    </revision>

    <revision>
    <revnumber>1.4</revnumber>
    <date>June 2000</date>
    <authorinitials>bk</authorinitials>
    <revremark>blub</revremark>  
    </revision>

    </revhistory>
    </para>
    </printhistory>

  </bookinfo>