code: def add_prefix(self, ncname: str) -> None:
          
          if ncname not in self.prefixmap:
              uri = cu.expand_uri(ncname + ':', self.curi_maps)
              if uri and '://' in uri:
                  self.prefixmap[ncname] = uri
              else:
                  print(f"Unrecognized prefix: {ncname}", file=sys.stderr)
                  self.prefixmap[ncname] = f"http://example.org/unknown/{ncname}/"
docs: Look up ncname and add it to the prefix map if necessary
  
          @param ncname: name to add