question: public void addPrefix ( String prefix , String namespaceURI ) { log . log ( Level . FINE , "addPrefix({0}, {1})" , new Object [ ] { prefix , namespaceURI } ) ; if ( prefix == null || namespaceURI == null ) { throw new IllegalArgumentException ( "Prefix or namespaceURI cannot be null!" ) ; } prefixToNamespace . put ( prefix , namespaceURI ) ; Set < String > prefixes = namespaceToPrefix . get ( namespaceURI ) ; if ( prefixes == null ) { prefixes = new HashSet < String > ( ) ; } prefixes . add ( prefix ) ; namespaceToPrefix . put ( namespaceURI , prefixes ) ; }
target:  Add a new prefix/namespace to the context.