How to assign a sequence to a variable?

Hi list,
I would like to return a sequence from a named
template, but I'm only getting a single string.
In the test only tempa gets the sequence, but how
to get it work for tempb and tempc?

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet version="2.0"
	xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
	<xsl:variable name="tempa" select="'a1','a2','a3'"/>
	<xsl:message select="$tempa[3]"/>
	<xsl:variable name="tempb">
		<xsl:value-of select="'b1','b2','b3'"/>
	</xsl:variable>
	<xsl:message select="$tempb[1]"/>
	<xsl:variable name="tempc">
		<xsl:call-template name="processName">
		</xsl:call-template>
	</xsl:variable>
	<xsl:message select="$tempc[1]"/>
</xsl:template>
<xsl:template name="processName">
	<xsl:value-of select="'c1','c2','c3'"/>
</xsl:template>
</xsl:stylesheet>

Regards, Manfred