[xsl] Making XPath expressions out of variables

This is a theoretical bit of XSL code which I need a practical version of:

All the variables are passed as parameters to the stylesheet.

<xsl:for-each select="//$record-type">
	<xsl:sort select="$sort-by" order="$sort-order" />
	<xsl:if test="$lh-operator $operand $rh-operator">
		<tr>
 			<xsl:for-each select="*">
				<td><xsl:value-of select="." /></td>
			</xsl:for-each>
		</tr>
	</xsl:if>
</xsl:for-each>

Any ideas? Is it possible? Or do I need to use this basic construct multiple 
times using <xsl:if> for each variable and the correct names of nodes and 
operands. (The number of permutations is massive!)

Cheers,
Richard
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This is question I was going to ask (it might make things clearer):

Is there a way of selecting nodes which have the name $some-variable using an 
XPath expression?

e.g. <xsl:for-each select="//$some-variable">

would, in theory (though not in practice - I've tried it!), select all the 
nodes whose name is equal to whatever the value of $some-variable is.
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