Written agreement presumed to contain all the terms of the agreement.
Section 285
SEC. 285. Written agreement presumed to contain all the terms of the agreement. — When the terms of an agreement have been reduced to writing by the parties, it is to be considered as containing all those terms, and therefore there can be, between the parties and their representatives or successors in interest, no evidence of the terms of agreement other than the contents of the writing, except in the following cases: 1. Where a mistake or imperfection of the writing, or its failure to express the true intent and agreement of the parties, is put in issue by the pleadings; 2. Where the validity of the agreement is the fact in dispute. But this section does not exclude other evidence of the circumstances under which the agreement was made, or to which it relates, or to explain an intrinsic ambiguity, or to establish its illegality or fraud. The term "agreement" includes deeds and instruments conveying real estate, and wills as well as contracts between parties.