code: def add_raw_code(self, string_or_list):
          
          if _is_string(string_or_list):
              self._GMSH_CODE.append(string_or_list)
          else:
              assert isinstance(string_or_list, list)
              for string in string_or_list:
                  self._GMSH_CODE.append(string)
          return
docs: Add raw Gmsh code.