Co robią modyfikatory -? i -readonly w mapped types?

type MakeRequired<T> = {
  [P in keyof T]-?: T[P];
};

type MakeMutable<T> = {
  -readonly [P in keyof T]: T[P];
};

interface Config {
  readonly host?: string;
  readonly port?: number;
}

type WritableConfig = MakeMutable<MakeRequired<Config>>;