Result Tree Fragment in Transformations (RTF)

Hi all, does anybody knows how to solve the issue with RTF on B1if?

Basically i what to pass an XML structure to a template an in that template receive that XLM as a parameter and iterate on it like this: 

<xsl:for-each select="$xml">      <xsl:value-of select="$xml/root1/root2"/>    </xsl:for-each>

Do i need to add any external library? If yes how can i do it?

Many thanks.