There are two sets of validation rules for drop-down menu fields. One set applies to fields that allow multiple selections, the other set applies to fields that allow only one selection.
If you configure a drop-down menu field to allow multiple selections, you can set a validation rule that requires at least one item to be selected when the user submits the form. You can further limit the use of the drop-down menu by specifying either a minimum or maximum number of allowable choices or both.
If you configure a drop-down menu field to allow one selection, you can set a validation rule that requires the user to make a choice.
A common trick in drop-down menus is to make the first choice an instruction, not a choice, as in the following menu: “Select seating preference, window, aisle, middle, any.” If you want to use this method in FrontPage, you can set a validation rule for either single or multiple-choice drop-down menu fields that prohibits the user from selecting the first item in the menu.