Luke Wroblewski has a great article on the various approaches for selection-dependent inputs. He clarifies what he means by selection-dependent inputs right in the beginning: Selection-dependent inputs are, in essence, a pretty simple concept: Once a user initially makes a selection from one or more options in a form, the user must provide additional input related to the selected option before submitting the form. … It’s worth pointing out that, in most cases, users cannot submit a form with selection-dependent inputs until they fill in the additional fields. [Continue]