A more thorough explanation:

The Fauntleroy Doctrine is a legal principle that requires a state to recognize and enforce a judgment made by another state, even if the claim on which the judgment is based is illegal in the state where enforcement is sought. This principle applies as long as the state that made the judgment had proper jurisdiction over the case.

For example, let's say that a person is sued in State A for breach of contract, and the court in State A finds in favor of the plaintiff and awards damages. If the plaintiff then tries to enforce the judgment in State B, but the contract at issue is illegal under State B's laws, the Fauntleroy Doctrine would require State B to still recognize and enforce the judgment from State A.

Another example could be a case where a person is granted a divorce in State A, but the grounds for divorce are not recognized as valid in State B. Even in this situation, State B would still be required to recognize and enforce the divorce decree under the Fauntleroy Doctrine.