code: public String childValue(String name, String namespace) {
          for (XNElement e : children) {
              if (Objects.equals(e.name, name) && Objects.equals(e.namespace, namespace)) {
                  return e.content;
              }
          }
          return null;
      }
docs: Returns the content of the first child which has the given name.
  @param name the child name
  @param namespace the namespace URI
  @return the content or null if no such child