docs: public static String getAttributeValue(final Node elementNode, final String attrName)
      {
          final Node attrNode = elementNode.getAttributes().getNamedItemNS(null, attrName);
  
          if (attrNode == null || "".equals(attrNode.getNodeValue()))
          {
              throw new IllegalStateException(
                  "Element '" + elementNode.getNodeName() + "' has empty or missing attribute: " + attrName);
          }
  
          return attrNode.getNodeValue();
      }