DOCBOOK: Inserting external code into docbook

[Joachim Ziegler <ziegler@algorilla.de>]

According to question 26 in the DocBook Markup FAQ, I tried the following:

------------------------------
(Bob Stayton says)

You can use following construct to include external code.

You only need the inlinemediaobject wrapper if you are using 4.1.2.

      <programlisting><inlinemediaobject>
          <textobject>
            <textdata fileref="yourfile.txt"/>
          </textobject>
        </inlinemediaobject></programlisting>
------------------------------

I am using 4.1.2 but I get the following errors:

Pythonbuch.xml:51: validity error: No declaration for attribute fileref on 
element textdata
            <textdata fileref="yourfile.txt"/>
                                            ^
Pythonbuch.xml:51: validity error: No declaration for element textdata
            <textdata fileref="yourfile.txt"/>
                                             ^
Pythonbuch.xml:52: validity error: Element textobject content doesn't follow 
the Dtd
Expecting (objectinfo? , (phrase | calloutlist | glosslist | itemizedlist | 
orderedlist | segmentedlist | simplelist | variablelist | caution | important 
| note | tip | warning | literallayout | programlisting | programlistingco | 
screen | screenco | screenshot | formalpara | para | simpara | blockquote+)), 
got (textdata )


What's the preferred way to include external program listings in a DocBook 
document?
BTW: I don't understand the semantics of the above nesting of elements.

Greetings,
joachim