code: @Override
      public void writeNamespace(String prefix, String nsURI)
          throws XMLStreamException
      {
          /* (see discussion in 'writeDefaultNamespace()' for details on
           * if and how this method may get called in repairing mode)
           */
          if (prefix == null || prefix.length() == 0) {
              writeDefaultNamespace(nsURI);
              return;
          }
          if (!mStartElementOpen) {
              throwOutputError(ERR_NSDECL_WRONG_STATE);
          }
          /* 01-Sep-2006, TSa: Let's only add the declaration if the prefix
           *   is as of yet unbound. If we have to re-bind things in future,
           *   so be it -- for now, this should suffice (and if we have to
           *   add re-binding, must verify that no attribute, nor element
           *   itself, is using overridden prefix)
           */
          int value = mCurrElem.isPrefixValid(prefix, nsURI, true);
          if (value == SimpleOutputElement.PREFIX_UNBOUND) {
              mCurrElem.addPrefix(prefix, nsURI);
              doWriteNamespace(prefix, nsURI);
          }
      }
docs: public void writeEmptyElement(String localName) throws XMLStreamException