When the language used in a document is, on its face, ambiguous or defective, evidence may not be given of facts which would show its meaning or supply its defects.
Illustrations
(a)A agrees, in writing, to sell a horse to B for “Rs. 1,000 or Rs. 1,500”. Evidence cannot be given to show which price was to be given.
(b)A deed contains blanks. Evidence cannot be given of facts which would show how they were meant to be filled.