question: @ Deprecated public void addPrefixNSMapping ( String prefix , String nsURI ) { if ( nsURI . length ( ) == 0 ) { throw new IllegalArgumentException ( "Cannot map empty string URI" ) ; } if ( prefix . length ( ) == 0 ) { throw new IllegalArgumentException ( "Cannot map empty string prefix" ) ; } if ( prefix . equals ( NO_NS_PREFIX ) ) { throw new IllegalArgumentException ( "The prefix: " + prefix + " cannot be registered, it's reserved for special internal use." ) ; } if ( prefixToNamespaceURILookup . containsKey ( prefix ) ) { throw new IllegalArgumentException ( "The prefix: '" + prefix + "' was repeated. This is illegal." ) ; } if ( namespaceURIToPrefixLookup . containsKey ( nsURI ) ) { throw new IllegalArgumentException ( "The namespace URI: " + nsURI + " cannot be mapped to 2 different prefixes." ) ; } if ( prefix . equals ( DEFAULT_NAMESPACE_PREFIX ) ) { this . defaultNS = nsURI ; } else { prefixToNamespaceURILookup . put ( prefix , nsURI ) ; namespaceURIToPrefixLookup . put ( nsURI , prefix ) ; } }
target:  This is used internally.