Where by any instrument coming into operation after the commencement of this Act an interest in any property is expressed to be given to the heir or heirs or issue or any particular heir or any class of the heirs or issue of any person in words which, but for this section would, under the rule of law known as the rule in Shelley’s Case, and independently of section 22 , have operated to give to that person an interest in fee simple or an entailed interest, such words shall operate as words of purchase and not of limitation, and shall be construed and have effect accordingly.