[xsl] Excluding an element with specific content from an <xsl:sort> call

["Mark Wilson" <mark@xxxxxxxxxxxx>]

Hi,
Is it possible when using <xsl:sort> to exclude elements with specific 
content from that <xsl:sort>call?

In Listing 1, when the content of the element<Prefix> is 'A' , I would like 
to exclude that particular element from being sorted in the <xsl:sort 
select="Prefix" data-type="text" /> call.  I cannot see how to use the 
"except" operator to do this. Is there a way to use "except" or some other 
filter?

Some input records will contain no <Prefix> element. However, when present, 
the <Prefix> element may content other than "A", such as "D", "L", etc. My 
goal is to sort input records with an <Prefix>A</Prefix> element as though 
it were absent from the record.

Listing 1:
<xsl:for-each-group select="Item" group-by="concat(CatalogName, Prefix, 
CatalogNumber, Range)">
<xsl:sort select="CatalogName" data-type="text" 
collation="{$sorting-collation}"/>
<xsl:sort select="Prefix" data-type="text" />
<xsl:sort select="CatalogNumber" data-type="number"/>

Thanks,
Mark