Linking a parent module option to options on child modules

To set the width value, you could present the options. However, you must set the width option once for each door. As the doors are identical for any given appliance, it would be better to set this value only once. You could create an Appliance Width option in the top level module and link this single option to all width options in the child modules. When the Appliance Width is set in the refrigerator freezer module, it propagates to the carcass module, to both door modules, the shelves, and so on. The link is referred to as a child module constraint.