question: private void register ( String key , Object value ) throws SAXException { if ( key != null ) { if ( _mapping . get ( key ) != null || ( _handler != null && _handler . hasVariable ( key ) ) ) { throw new SAXException ( "ID " + key + " is already defined" ) ; } if ( _handler != null ) { _handler . setVariable ( key , value ) ; } else { _mapping . put ( key , value ) ; } } }
target:  Registers an object by name. This will throw an exception if an object has already been registered under the given name.