Thank you Kevin. You're suggestions have led to a query that works for me.
I wanted to transform an XML file into an interactive form, where users could "SELECT " arbitrary descriptive tags, inside the XML, and then transform the chosen criteria into an xpath query, on the fly.
That's why I was searching for a way to concatentate arbitrary lists of xpaths into one query. What works for me, which I doped out from what you posted (thank you):
$XINDICE_HOME/bin/xindice xpath -l -c /db/neurosys/data -q "/XSIL[
//[EMAIL PROTECTED]'DIRECTIONAL_TUNING']/[EMAIL PROTECTED]'value'][text()='262'] and /XSIL/[EMAIL PROTECTED]'system']/[EMAIL PROTECTED]'owner'][text()='gwen']]/[EMAIL PROTECTED]'system']"
$XINDICE_HOME/bin/xindice xpath -l -c /db/neurosys/data -q "/XSIL[XSIL/XSIL/XSIL/XSIL/XSIL/[EMAIL PROTECTED]'DIRECTIONAL_TUNING']/[EMAIL PROTECTED]'value'][text()='262'] and /XSIL/[EMAIL PROTECTED]'system']/[EMAIL PROTECTED]'owner'][text()='gwen']]/[EMAIL PROTECTED]'system']"
-- /* Sandy Pittendrigh >--oO0> * [EMAIL PROTECTED] * http://cns.montana.edu/~sandy */
