node-set Function
Enables you to convert a tree into a node set. The resulting node always contains a single node and the root node of the tree.
msxsl:node-set(string)
Remarks
With earlier versions of Microsoft® XML Core Services (MSXML), it was possible to use expressions such as <xsl:for-each select="$var/el">, where var is an XSLT variable bound to a result tree. However, this approach does not work with MSXML versions 3.0 and later. To achieve the same results in these more recent version of MSXML, use the node-set function, as shown in the following code sample.
<xsl:for-each select="msxsl:node-set($var)/el)">