I am setting up a courier service that allows customers to place and pay for online delivery services, but only want certain options available if they change their service type... for example, if they select "Envelope" as the package type, I don't want them to have to enter dimensions of the package unless they select "Small Box", "Medium Box", or "Large Box" at which point, selecting any of the "Box" Package Types would now reveal the Dimensions input fields.
