Relating to an exemption from ad valorem taxation by a school district of a portion of the appraised value of a residence homestead based on the median market value of all residence homesteads in this state, a reduction of the limitation on the total amount of ad valorem taxes that may be imposed by a school district on the homestead of an elderly or disabled person to reflect any increase in the exemption amount, and the protection of school districts against any resulting loss in local revenue.