[fendy3002]

Not OP, but it's useful for if:

- something is done to object when some props is set or validation, such as .withStuffedCrust("cheese"), it'll set the internal props as crust="stuffed" and stuffContent="cheese"

- it's branching. So rather than making user looking for the components or configuration themselves, library author can guide them with builder. Such as:

  myVehicleBuilder.withSixTires().withTrailerAttachment().attach(container)

In this case withTrailerAttachment (and possibly withOpenBack or withBox) won't show up if you call withTwoTires(), and attach won't show up if you don't call withTrailerAttachment().