Converting <xml> StyleSheet param contents into a node

HI all, can somebody tell me how I can pass <xml> contents into a
stylesheet param and then convert that <xml> contents into a nodeset?


Stylesheet: ( Filter=<Node><Whatever/></Node> )
...
<xsl:param name="Filter" select="string('NULL')" />

   <xsl:copy-of select="$Filter"/>
...
Output:
   &lt;Node&gt;&lt;Whatever/&gt;&lt;/Node&gt;

However, I want to turn the xml contents above into a node set that I
can later use in the transform.  Is that possible (is there something
other than using CDATA)?

Any information would be greatly appreciated.