Section 48 of Evidence Act "Opinion as to existence of right or custom, when relevant"
When the Court has to form an opinion as to the existence of any general custom or right, the opinions, as to the existence of such custom or right, or persons who would be likely to know of its existence if it existed, are relevant.
Explanation The expression "general custom or right" includes customs or rights common to any considerable class of persons.
Section 49 of Evidence Act "Opinion as to usage, tenets, etc., when relevant"
When the Court has to form an opinion as to-
the usages and tenets of any body of men or family, the constitution and government of any religious or charitable foundation, or
the meaning of words or terms used in particular districts or by particular or by particular classes of people, the opinions of persons having special means of knowledge thereon, we relevant facts.
Section 50 of Evidence Act "Opinion on relationship, when relevant"
When the Court has to form an opinion as to the relationship of one person to another, the opinion expressed by conduct, as to the existence of such relationship, of any person who, as a member of the family or otherwise, has special means of knowledge on the subject, is a relevant fact:
Provided that such opinion shall not be sufficient to
prove a marriage in proceedings under the India Divorce Act,
1869 (4 of 1869) or in prosecutions under sections 494, 495,
497 or 498 of the Indian Penal Code, (45 of 1960)
Illustrations
(a) The question is, whether A and B, were married.
The fact that they were usually received and treated by
their friends as husband and wife, is relevant.
(b) The question is, whether A was the legitimate son of B.
The fact that A was always treated as such by members of the
family, is relevant.
Illustration
An expert may give an account of experiments performed by
him for the purpose of forming his opinion.