Execute the function. The function must return
a valid object.
DTMIterator nodes = m_arg0.asIterator(xctxt, xctxt.getCurrentNode());
double sum = 0.0;
int pos;
while (DTM.NULL != (pos = nodes.nextNode()))
{
DTM dtm = nodes.getDTM(pos);
XMLString s = dtm.getStringValue(pos);
if (null != s)
sum += s.toDouble();
}
nodes.detach();
return new XNumber(sum);