[xslt] xsl:param works only with numbers as content

["Stephan Otte" <Stephan Otte pcc de>]

Hello,
I have a problem with stylesheet-parameters whose content  are not numbers.
The value of them in the result tree is empty!
Stylesheet:
...
<xsl:param name="user">nobody</xsl:param>

<xsl:template match="/">
user: <xsl:value-of select="$user"/>
....

I pass the parameters with "xsltproc --param user stephan" or use the default in
the
stylesheet by omitting it in the command line, the result is the same.
If the content is a number, everything works!

Any help?

Stephan