Reproduce process¶ irb(main):002:0> require 'date' => true irb(main):003:0> Date.new(2019, 5, 1).jisx0301 => "H31.05.01" ruby version: trunk Result of reproduce process¶ irb(main):003:0> Date.new(2019, 5, 1).jisx0301 => "H31.05.01" Expected result and the reason why you expect¶ irb(main):002:0> require 'date' => true irb(main):003:0> Date.new(2019, 5, 1).jisx0301 => "R01.05.01" reason¶ new era (Re