code: public void declarePrefix(String prefix, String uri){
          if(prefix.length()==0)
              defaultURI = uri;
          prefix2uriMap.put(prefix, uri);
          uri2prefixMap.put(uri, prefix);
      }
docs: Binds specified {@code prefix} to the given {@code uri}
  
  @param prefix the prefix to be bound
  @param uri the uri to which specified {@code prefix} to be bound