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 “one lakh rupees or one lakh fifty thousand rupees”. 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.