law: Indian Evidence Act, 1872 
  48. 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.
  Illustrations
  The right of the
  
  villages of a particular village to use the water of a particular well is a
  
  general right within the meaning of this section.