I want to evaluate a XPath-Expression only on a subtree of the whole
xml-document.

1. I select a node of the XML-document
2. Then a want to select specific nodes below the node chosen in 1.

I thought the parameter contextNode in
var xpathResult = document.evaluate(xpathExpression, contextNode,
namespaceResolver, resultType, result)
would do this like described here
http://www-xray.ast.cam.ac.uk/~jgraham/mozilla/xpath-tutorial.html

But this doesn't work. It still selects all nodes from the whole
document and not only of the subtree.

At the bottom is a short example.

The XML-Document:
<gods>
        <god name="Kibo">
                <amount value="3"/>
        </god>
        <god name="Xibo">
                <amount value="6"/>
        </god>
<\/gods>

1. I select the node <god name="Kibo"> and name it godKibo.
2. I want to get the nodelist of all <amount>-Nodes below godKibo.
var expr = '//amount';
var xpathResult = xmlDocument.evaluate(
        expr,
        godKibo,
        null,
        XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE,
        null
);

But this gives a list of all <amount>-Nodes of the document. How do I
have to change expr to work?

I know if I set:

var expr = '//god[@name="Kibo"]/amount';
var xpathResult = xmlDocument.evaluate(
        expr,
        xmlDocument,
        null,
        XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE,
        null
);

it will work. But I don't want to repeat the expression to find the
godKibo-node.

Thanks for your help.

Greetings,
   Björn

Here is the full example.

var xmlSource = '';
xmlSource += '<gods>';
xmlSource += '<god name="Kibo">';
xmlSource += '<amount value="3"/>';
xmlSource += '</god>';
xmlSource += '<god name="Xibo">';
xmlSource += '<amount value="6"/>';
xmlSource += '</god>';
xmlSource += '<\/gods>';
var xmlDocument = new DOMParser().parseFromString(xmlSource, 'text/xml');

var xmlSerializer = new XMLSerializer();

// Selecting the node god with the name Kibo

var godKibo = xmlDocument.evaluate(
        '//god[@name="Kibo"]',
        xmlDocument,
        null,
        XPathResult.FIRST_ORDERED_NODE_TYPE,
        null
).singleNodeValue;

// Selecting the node amount below the node godKibo

var expr = '//amount';

var xpathResult = xmlDocument.evaluate(
        expr,
        godKibo,
        null,
        XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE,
        null
);

// This alert returns 2 although I thought it would
// search only below the godKibo node and return 1

--