Is it permissible for a woman to marry her husband informally ( عرفيًا ) before the 'iddah period ends?

If a woman is undergoing the waiting period (iddah) after a revocable divorce, her husband may take her back without a new contract. If the divorce is an irrevocable minor divorce, he may take her back during her waiting period with a new contract. However, if it is the third divorce, she is not lawful for him until she marries another husband, as Allah the Almighty says: "And if he has divorced her [for the third time], then she is not lawful to him afterward until she marries another husband." An urfi marriage is valid if it fulfills the conditions of a lawful marriage.