IEA Section 50

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, or any person who, as a member of the family or otherwise, has special means of knowledge on the subject, is relevant fact;
Provided that such opinion shall not be sufficient to prove a marriage in proceedings under the Indian Divorce Act, 1869 (4 of 1869) or in prosecutions under sections 494, 495, 497 or 498 of the Indian Penal Code (45 of 1860).