When language used in a document is, on its face, ambiguous of defective, evidence may not be given of facts which would show its meaning or supply its defect.
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 not show how they were meant to be filled.