DOCBOOK-APPS: Textobject and Alt tag

The textobject is not rendered at all, what is wrong? I want it to be
rendered as an alt tag!

<!DOCTYPE Article PUBLIC "-//OASIS//DTD DocBook V4.1//EN">
<Article lang="no">

<articleinfo>
<mediaobject>
      <imageobject>
	<imagedata  Fileref="./logo.png" align="center">
      </imageobject>
      <TextObject>
        <phrase>Alt tag</phrase>
      </textobject>
    </mediaobject>

I've also tried to move the image to another place in the document,
but with the same result.
Lars
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Lars Bj鷨ndal <>
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