docs: public boolean hasAttr(String attributeKey) {
          Validate.notNull(attributeKey);
  
          if (attributeKey.startsWith("abs:")) {
              String key = attributeKey.substring("abs:".length());
              if (attributes().hasKeyIgnoreCase(key) && !absUrl(key).equals(""))
                  return true;
          }
          return attributes().hasKeyIgnoreCase(attributeKey);
      }