code: public static String readStringAttributeElement(final XMLStreamReader reader, final String attributeName)
              throws XMLStreamException {
          final String value = requireSingleAttribute(reader, attributeName);
          requireNoContent(reader);
          return value;
      }
docs: Read an element which contains only a single string attribute.
  @param reader the reader
  @param attributeName the attribute name, usually "value" or "name"
  @return the string value
  @throws javax.xml.stream.XMLStreamException if an error occurs or if the
  element does not contain the specified attribute, contains other
  attributes, or contains child elements.