Task: Question Generation
Input (English): Significant legislative changes in the status of the szlachta, as defined by Robert Bideleux and Ian Jeffries, consist of its 1374 exemption from the land tax, a 1425 guarantee against the 'arbitrary arrests and/or seizure of property' of its members, a 1454 requirement that military forces and new taxes be approved by provincial Sejms, and statutes issued between 1496 and 1611 that prescribed the rights of commoners.
Output (English): Who defined the significant legislative changes?