Section 101

Persons who are not parties to a document or their representatives in interest may give evidence of any fact tending to show a contemporaneous agreement varying the terms of the document.Illustration A and B make a contract in writing that B is to sell A certain tin to be paid for on delivery. At the same time they make an oral agreement that 3 months’ credit is to be given to A. This could not be shown as between A and B, but it might be shown by C if it affected C’s interests.