What is "official purpose"?

The same article I quoted just previously raises, apparently, an important constitutional issue in the Real ID law. Apparently Real ID cards will be required for federal "official purposes," but that term is undefined in the law. The term could be interpreted to mean that you can not vote in a federal election without a Real ID card. (Such an interpretation would probably be unconstitutional, as the courts have repeatedly struck down laws that make it signifigantly harder to qualify to vote.) But basically, without a definition of the term, it's impossible to anticipate who must buy equipment and pay guards to enforce the law.

In any case, many definitions of "official purpose" will require each state to bite the cost of supplying Real ID cards to far more people than registered drivers. And it's clear states will be losing money to supply these cards unless they are incredibly expensive.