The Federal Rules of Evidence is a set of rules which regard the manners in which evidence might be allowed into trials, and might function within trials, within the federal court system, specifically. 

The Federal Rules of Evidence do not, thus, control the rules of evidence with regard to state courts, as each state is free to adopt its own rules of evidence which might differ from the Federal Rules of Evidence, although most states ultimately adopted evidence-based rules which are based on the Federal Rules of Evidence. 

The Federal Rules of Evidence are designed to provide a fair and balanced basic framework in which the jury can understand how it should be considering different pieces of evidence, and what exact evidence should be allowed into consideration.

The Federal Rules of Evidence include rules concerning any evidence about a given individual’s prior crimes, which state that considering those crimes is not allowed in terms of considering the crime or issue at stake in the current trial, unless those previous crimes are somehow directly relevant, and they also include rules concerning the admission of hearsay into the trial, as hearsay might sometimes be an important piece of testimony, but it is often disallowed.

The Federal Rules of Evidence were adopted fully in 1975 under the Act to Establish Rules of Evidence for Certain Courts and Proceedings. The Federal Rules of Evidence do not often set out the punishments for violations of the Federal Rules of Evidence.

The parol evidence rule is a law of evidence which is designed to support the validity of an obvious written contract over any other evidence, assuming that the written contract does not appear to have been tampered with or made falsely, and does appear to be complete and in effect. 

The parol evidence rule would thus concern situations in which an individual claims that an oral conversation took place which provided terms for the agreement in question which might have been different from the terms proposed on the actual contract. In such a case, the parol evidence rule would act as a law of evidence and would disallow the evidence of the oral conversation, as the written document would override the written conversation.

The parol evidence rule makes several important distinctions which are important to understand in order to fully realize how it is applied as a law of evidence. The parol evidence rule, for example, sets out that the contract under consideration must be absolutely final and complete for the parol evidence rule to apply in full. 

If the contract is partial, and is not complete, then this law of evidence would apply in terms of disallowing evidence outside of the contract which might contradict the written document, but it would not act as a law of evidence in preventing the introduction of evidence which added to the contract. A full contract, under the parol evidence rule, inherently disallows the introduction of any evidence which would alter the contract in any way.