Contracts-Parol Evidence Rule

If there is a written agreement,

negotiations, understandings, agreements reached prior to or contemporaneous with the written agreement are

ALWAYS admissible to show that the K was subject to an oral condition precedent
ALWAYS admissible to EXPLAIN
INADMISSIBLE to contradict if the written K is integrated with respect to that term
INADMISSIBLE to supplement if the written K is a complete integration of the bargain.

Exception: the evidence shows a collateral agreement -- a whole separate stand-alone agreement.