The Federal Rules of Evidence govern the admissibility of evidence in diversity cases. Johnson v. William C. Ellis & Sons Iron Works, Inc., 609 F.2d 820 (5th Cir. 1980). Federal law also controls all other procedural matters in diversity cases. See, e. g., Southern Pacific Transportation Co. v. Smith Material Corp., 616 F.2d 111 (5th Cir. 1980).