Final answer:
The requirement for Nevada's marriage to be recognized in Idaho is an application of the Full Faith and Credit Clause of the Constitution, which ensures states honor each other's legal documents and proceedings.
Step-by-step explanation:
The fact that a marriage in the state of Nevada must be honored in Idaho is an example of the constitutional provision known as the Full Faith and Credit Clause. This clause is found in Article IV, Section 1 of the United States Constitution and requires states to respect the public acts, official records, and judicial proceedings of every other state. With this clause, legal documents such as marriage certificates are acknowledged across state lines, ensuring consistency and order in interstate relations.