code: public long longValue(String name, String namespace) {
          String s = childValue(name, namespace);
          if (s != null) {
              return Long.parseLong(s);
          }
          throw new IllegalArgumentException(this + ": content: " + name);
      }
docs: Returns a long value of the supplied child or throws an exception if missing.
  @param name the child element name
  @param namespace the element namespace
  @return the value