what does it mean if a term is collateral to a written agreement
Parol evidence rule To put it simply, (1) If the parties intend a complete integration of the contract terms, no parol evidence within the scope of agreement is permitted. (2) If the parties intended a partial integrated agreement, no parol evidence that contradicts anything integrated is permitted. And (3), if the parol evidence is collateral, meaning it regards a different agreement, and does not contradict the integrated terms, and are not terms any reasonable person would always naturally integrate, then the rule does not apply and the evidence is admissible.