if (expr == null || expr.length() == 0)
return Double.NaN;
NodeSetDTM contextNodes = new NodeSetDTM(nl, xctxt);
xctxt.pushContextNodeList(contextNodes);
double maxValue = - Double.MAX_VALUE;
for (int i = 0; i < contextNodes.getLength(); i++)
{
int contextNode = contextNodes.item(i);