If.. then…
Consider this scenario: A form that lets you pay by credit card or by money order. If credit card is selected, then all associated fields (card type, number, etc) would be REQUIRED, but if money order was chose, then the credit card fields would NOT be required.
At least one and possibly both, or at least one and only one…
Consider this scenario: A contact form that asks for ‘State’ - it gives you a drop down list of all the states in America, AND an option to enter text for those outside America.
In this case, at least one of those two fields would be required, but not both.
