> <xsl:variable name="contemporaries" select="//person[@age=$age]"/>
>
> Sum their incomes:
>
> sum($contemporaries/group/@income)

That should probably be sum($contemporaries/parent::group/@income)


>> <cutomers>
>>        <group income=1000>
>>                <person age=10/>
>>                <person age=15/>
>>                <person age=30/>
>>        </group>
>>
>>        <group income=2000>
>>                <person age=10/>
>>                <person age=40/>
>>        </group>
>>
>>        <group income=5000>
>>                <person age=20/>
>>                <person age=20/>
>>        </group>
>> </customers>




-- 
Andrew Welch
http://andrewjwelch.com
Kernow: http://kernowforsaxon.sf.net/