You have namespace in the xml so either we use that or there is a shorthand that you can try, instead of xml_ns use a *. So instead of "xml_ns:" use can use "*:", then you don't need to specify -> with xmlnamespaces...
You have namespace in the xml so either we use that or there is a shorthand that you can try, instead of xml_ns use a *. So instead of "xml_ns:" use can use "*:", then you don't need to specify -> with xmlnamespaces...