(a) A governmental body with taxing authority that issues a written determination letter, technical advice memorandum, or ruling that concerns a tax matter shall index the letter, memorandum, or ruling by subject matter.
(b) On request, the governmental body shall make the index prepared under Subsection (a) and the document itself available to the public, subject to the provisions of this chapter.

(c) Subchapter C does not authorize withholding from the public or limiting the availability to the public of a written determination letter, technical advice memorandum, or ruling that concerns a tax matter and that is issued by a governmental body with taxing authority.