" In support of their arguments, plaintiffs cited, inter alia , an opinion of the Texas Attorney General in which, according to plaintiffs, the attorney general "concluded that benefits protected by the constitution 'necessarily include the dollar amount of the benefits payable at retirement.' " See Tex. Att'y Gen. Op. No. GA–0615, 2008 WL 982266 (2008). Defendants argued in the trial court as follows: (1) "based on the modifying terms, Section 66 limits the definition of benefits to be accorded protection to three types," i.e., "service retirement benefits," "disability retirement benefits," and "death benefits"; (2) "[b]ecause there is no allegation that the Plan Amendments at issue affect disability retirement or death benefits, this leaves only the question of whether DROP falls under the definition of 'service retirement benefits' "; (3) "DROP is not a 'service retirement benefit' under Section 66"; (4) "[b]ecause Section 66 does not define 'service retirement benefit,' the [trial court] must look to other sources"; (5) "[t]he best source is the statutory provision that enabled and governs the rules and structure of the Dallas Police and Firefighter Pension Fund: Article 6243a–1"; (6) sections 6.01 and 6.02 of that article "define traditional monthly retirement pension benefits (aka, 'service retirement benefits')"; (7) Section