Effect of non-registration of documents required to be registered

No document required by section 17 1[or by any provision of the Transfer of Property Act, 1882 (4 of 1882)], to be registered shall— (a) affect any immovable property comprised therein, or (b) confer any power to adopt, or (c) be received as evidence of any transaction affecting such property or conferring such power, unless it has been registered: 1[Provided that an unregistered document affecting immovable property and required by this Act or the Transfer of Property Act, 1882 (4 of 1882), to be registered may be received as evidence of a contract in a suit for specific performance under Chapter II of the Specific Relief Act, 1877 (1 of 1877)1, 2*** or as evidence of any collateral transaction not required to be effected by registered instrument.]