code: def update(self, name: str, value=None, default=None, description: str=None):
          
          if name in self._vars:
              description = description or self._vars[name].description
              default = default or self._vars[name].default
          elif name == 'name':
              raise ConfigError("'name' is a reserved name for a group.")
  
          v = _Var(name, description=description, default=default, defined=False)
          v.value = value
          self._vars[name] = v
docs: Like add, but can tolerate existing values; also updates the value.
  
          Mostly used for setting fields from imported INI files and modified CLI flags.