code: @Override
      public void writeAttribute(String localName, String value)
          throws XMLStreamException
      {
          // No need to set mAnyOutput, nor close the element
          if (!mStartElementOpen && mCheckStructure) {
              reportNwfStructure(ErrorConsts.WERR_ATTR_NO_ELEM);
          }
          doWriteAttr(localName, null, null, value);
      }
docs: It's assumed calling this method implies caller just wants to add
  an attribute that does not belong to any namespace; as such no
  namespace checking or prefix generation is needed.