"Due process of law" is a concept that originated in English common law and can be succinctly described as fundamental fairness of judicial process. It includes the right to petition a court for redress of grievances, right to call witnesses and right to face one's accuser. The Bill of Rights requires the federal government grant citizens and non-citizens due process of law. Due process was applied to state governments through the 14th Amendment of the U.S. Constitution and has since been included in the statutory and constitutional law of every state.
Florida Rule 1.540
Rule 1.540 protects due process by allowing aggrieved parties to dispute and potentially obtain reversal of "final" judicial actions, including divorce decrees that are unfair either because of innocent mistakes, such as clerical errors, or because of culpable misconduct, such as negligence or deliberate fraud. You don't have to be a party to a divorce action to benefit from Rule 1.540. Anyone adversely affected by a judicial action, such as a minor child of divorced spouses, may file a petition for reversal of a judicial action under Rule 1.540.
Evidence establishing fraud or mistake incidental to a judicial proceeding is not enough to reverse a judicial action under Rule 1.540. You must also establish "prejudice." This requires presenting evidence showing it is more likely than not that the judicial action you are protesting would not have occurred absent the fraud or mistake. For example, if custody of a minor child was awarded to a father who concealed evidence of an addiction to pornography, you must establish that if the evidence had surfaced during the custody hearing, the court probably would not have awarded custody to the father.
In addition to showing prejudice, a petitioner under Rule 1.540 must show that he was damaged by the judicial action he seeks to overturn. In Romero v. Romero, a divorced wife sought to set aside a property settlement using Rule 1.540. Although she successfully established that her husband had failed to disclose the existence of stock options that had been awarded to him and although the trial court determined the stock options were marital property, the appeals court denied her motion to set aside the property settlement because she failed to establish her claims that if she had known about the stock options, she not only would have claimed half, but she would have also exercised and sold them then used the proceeds to pay her mortgage.