When the court has to form an opinion as to the person by whom any document was written or signed, the opinion of any person acquainted with the handwriting of the person by whom it is supposed to be written or signed that it was or was not written or signed by that person is a relevant fact.

Explanation."A person is said to be acquainted with the handwriting of another person when he or she has seen that person write, or when he or she has received documents purporting to be written by that person in answer to documents written by himself or herself or under his or her authority and addressed to that person, or when, in the ordinary course of business, documents purporting to be written by that person have been habitually submitted to him or her.