Returns the text value of the child node with the given local name and namespace.
CL_DomString CL_DomElement::get_child_string_ns( const CL_DomString & namespace_uri, const CL_DomString & local_name, const CL_DomString & default_value = CL_DomString ());
Detailed description:
Finds the first child node with the specified local name and namespace, then returns the content of its first child text node