Expansion Tank

I live in the southeast where about 25% of homes have gas water heaters.
(Florida) are all gas water heaters required to have expansion tank if so where is proper placement of the tank?

ALL water heaters. On the cold supply, best after the valve.

I have done over 11,000 inspections here in San Diego and today came across just the second expansion tank ever here. The plumbers don’t mind not installing them and the AHJ’s don’t mind them missing.