>it works fine with <xsl:sort select="*[name()='article_price']" />
It would work even finer with <xsl:sort select="article_price"/>
>But I don´t know what to do to sort the articles for example by the <value> of <article_group>´s with the <name>Quality</name>.
<xsl:sort select="article_groups/article_group[name='Quality']/value"/>
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference