[xsl] Newbie question on XSL transformations: multiple sorts on element attributes

[Rob Newman <rlnewman@xxxxxxxx>]

Hi there,

I am relatively new to XSL transformations, so I apologize in advance  
if this question seems ridiculously simple. I have an XML file in the  
following format (which I cannot control):

<?xml version="1.0" encoding="iso-8859-1"?>
<pfarr name="xyz">
	<pfarr name="dls">
		<pfarr name="abcde">
			<pfstring name="aa">0.010</pfstring>
			<pfstring name="br24">23266128.0</pfstring>
			<pfstring name="dlt">20</pfstring>
			...... (lots of other pfstring elements)
		</pfarr>
	</pfarr>
</pfarr>

XSLT:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/ 
Transform">

<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes" />

<xsl:template match="sources">
	<xsl:element name="dataloggerlist">
		<xsl:for-each select="source">
			<xsl:apply-templates select="/pfarr/pfarr/pfarr" />
		</xsl:for-each>
	</xsl:element>
</xsl:template>

<xsl:template match="pfarr/pfarr/pfarr">
	<xsl:element name="datalogger">
		<xsl:attribute name="name"><xsl:value-of select="@name"/></ 
xsl:attribute>
		<xsl:apply-templates select="pfstring"/>
	</xsl:element>
</xsl:template>

<xsl:template match="pfstring">
	<xsl:element name="param">
		<xsl:attribute name="id"><xsl:value-of select="@name"/></ 
xsl:attribute>
		<xsl:value-of select="." />
	</xsl:element>
</xsl:template>

</xsl:stylesheet>

Resulting XML:

<?xml version="1.0" encoding="UTF-8"?>
<dataloggerlist>
	<datalogger name="TA_A04A">
		<param id="aa">0.010</param>
		<param id="br24">23266128.0</param>
		<param id="dlt">20</param>
		.......
	</datalogger>
</dataloggerlist>

This is great and what I want my output to look like. However, I want  
to sort the XML output on (1) the id = 'dlt' attribute param element,  
and (2) the datalogger element name attribute. Can I do this in the  
same XSL file, or do I need to create another XSL file to transform  
the XML I just created? I have tried several approaches at taking my  
XML output and applying another XSL transformation (and creating a  
new XML file), such as:

-- START SNIPPET --
<xsl:template match="dataloggerlist">
	<xsl:element name="dataloggerlist">
		<xsl:apply-templates select="datalogger">
			<xsl:sort select="param/@id{dlt}" data-type="number"  
order="descending" />
			<xsl:sort select="@name" order="ascending" />
		</xsl:apply-templates>
	</xsl:element>
</xsl:template>
-- END SNIPPET --
(Note: the datalogger template outputs the data same as before)

This sorts the output on datalogger name (50% correct), but not the  
param element id = 'dlt'. I am sure this is just a simple syntax  
issue, and I have searched online for examples, but none seem to show  
sorts on specific element ids. I have Jeni Tennison's 'Beginning  
XSLT' and have scoured the chapter on Sorting, but I can't seem to  
figure it out. I would prefer to do this whole process in one step,  
and avoid having two XSL files that create an interim XML file that  
just gets transformed again. Any help would be most appreciated.

Thanks in advance,
- Rob