fun optional(defaultValue: T? = null): BasicDerAdapter<T> = copy(isOptional = true, defaultValue = defaultValue)

  /**
   * Returns a copy of this adapter that sets the encoded or decoded value as the type hint for the
   * other adapters on this SEQUENCE to interrogate.
   */
  fun asTypeHint(): BasicDerAdapter<T> = copy(typeHint = true)