Opinions of experts:

When the Court has to form an opinion upon a point of foreign law, or of science/or art, or as to identity Of hand-writing or finger impressions; the opinions upon that point of persons specially skilled in such foreign law science or art, or in questions as to identity of hand-writing or finger impressions-are relevant facts.  
Such persons are called experts.  
Illustrations  
(a) The question is, whether the death of A was caused by poison The opinion of experts as to the symptoms produced by the poisoned which A is supposed to have died, are relevant.  
(b) The question is, whether A, at the time of doing a certain act, was by reason of unsoundness of mind, incapable of knowing the nature of the apt, or that he was doing what was either wrong or contrary to law.  
Thee opinions of experts upon the question whether the symptoms exhibited by A commonly show unsoundness of mind, and whether such unsoundness of mind usually renders persons incapable of knowing the nature of the acts which they do, or of knowing that what they do either wrong or contrary to law are relevant.  
(c) The question is whether a certain document was written by A, Another document is produced which is proved or admitted to have been written by A.  
The opinions of experts on the question whether the two documents were written by the same person or by different persons are relevant.  

Facts bearing upon opinions of experts:

Facts not otherwise relevant, are relevant if they support or are inconsistent with the opinions of experts, when such opinion are relevant.  
Illustrations

(a) The question is, whether A was poisoned by a certain poison The fact that other persons, who were poisoned by that poison, exhibited certain symptoms which experts affirm or deny to be the symptoms that poison, is relevant.  
(b) The question is, whether an obstruction to a harbour is caused by a certain sea wall.  
The fact that other harbours similarly situated in other respects, but where there were no such sea-walls, began to be obstructed at about the same time, is relevant.  

Opinion as to hand-writing when relevant:

When the Court has to form an opinion as to the person by whom any document was written or signed, the opinion of any parson acquainted with the hand-writing of the person by whom it is supposed to be written or signed that it was or it was not written or signed by that person, is relevant fact.  
Explanation: A person is said to be acquainted with the hand-writing of another person when he has seen that person write, or when he has received documents purporting to be written by that person in answer to documents written by himself or under his 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.          -.                              
Illustrations:

The question is whether a given letter is m the handwriting of A, a merchant in London.  B is a merchant in Peshawar, who has written letters addressed to A and received letters purporting to be written by him, C is B's clerk, whose duty it was to examine and file B’s correspondence. D is B's broker, to whom B habitually submitted the letters purporting to be written by A for the purpose of advising him thereon.           '  
The opinion of B, C and D on the question whether the letter is in the handwriting of A are relevant though neither B, C or D ever saw A write.  

Opinion as to existent 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 opinion, as to the existence of such custom or right, of 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.  
Illustrations: The right of the villagers of a particular village to use the water of a particular well is a general right within the meaning of this Article.  
 

Opinion as to usages, tenets, etc., when relevant:

When the Court has to form an opinion as to—  
the usages and tenets of any body of man 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 classes of people,  
the opinions of persons haying special means of knowledge thereon, are relevant facts.  
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 Divorce Act 1869 (IV of 1869), or in prosecutions under Section 494 or 495 of the Pakistan Penal Code (Act XIV of 1860).  
Illustrations:

(a) The question is whether A and B were married.  
The fact they were usually received and treated by their friends as husband and wife, it 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.  

Grounds of opinion when relevant:

Whenever the opinion of any living person is relevant, the grounds on which such opinion is based are also relevant.  
Illustration: 

An expert may give an account of experiments performed by him for the purpose of forming his opinion.