The snippet below attempts to split the string 'mileage 6' into
[mileage] and [6] and then store it in $miles (for example).

I am trying to get the SUM of the resulting SPLIT of the nodes that
match 'mileage'.

<xsl:variable name="miles">
	<xsl:call-template name="str-split-to-words">
		<xsl:with-param name="pStr"
select="msxsl:node-set($expenses[substring(expense,1,7)='mileage']/expense)"
/>
		<xsl:with-param name="pDelimiters" select="' '" />
                                     <!-- splitting expense at blank spaces -->
	</xsl:call-template>
</xsl:variable>
<xsl:value-of select="msxsl:node-set($miles)/*[2]" /><br />

<Expenses>
   <expense>Mileage 6</expense>
   <expense>cheese</expense> (wouldn't match)
   <expense>Mileage 10</expense>
</Expenses>