How to handle TAB's in FOP?

I have exported a block of text and tried to reform it with XSL-FOP to PDF.

example of the content:
<ArticleTx>
Aansluitingen:
Aanvoer		: 1¼" buitendraad.
Retour		: 1¼" buitendraad.
Gas		 	: 1¼" buitendraad.
Rookgasafvoer	: Ø 150 mm.
Luchttoevoer	: Ø 150 mm (indien gesloten uitgevoerd).
Condensafvoer	: Ø  32 mm uitwendig.
</ArticleTx>

This is the way they are treated:

<!-- Aanvullende artikeltekst afdrukken -->
<xsl:if test="ArticleTx!=''">
	<fo:block white-space-collapse="false" space-before="0.5cm"
end-indent="1.5cm">
		<xsl:value-of select="ArticleTx"/>
	</fo:block>
</xsl:if>

It contains RETURN's and TAB's. To handle RETURN's is not the problem: just
replace them with a charactercode. But the TAB's are giving me more
problems! Does anyone know how to handle the TAB's? I tried to replace them
with &#9; but that does not solve the problem. One TAB is larger (4 spaces)
then the other TAB (9 spaces), so there is not a well formed output.

Who can help me?

Thx!

Henk Gootjes
Delias IT