law: Indian Stamp Act, 1899 
  4. Several instruments used in single transaction of sale,
  
  mortgage or settlement 
  (1) Where, in the case of any sale, mortgage or settlement,
  
  several instruments are employed for completing the transaction, the principal instrument
  
  only shall be chargeable with the duty prescribed in Schedule I, for the
  
  conveyance, mortgage or settlement, and each of the other instruments shall be
  
  chargeable with a duty of one rupee instead of the duty (if any) prescribed for
  
  it in that Schedule.
  (2) The parties may determine for themselves which of the
  
  instruments so employed shall, for the purposes of sub-section (1), be deemed
  
  to be the principal instrument:
  PROVIDED  that the duty chargeable on the instrument so
  
  determined shall be the highest duty which would be chargeable in respect of
  
  any of the said instruments employed.