mutable?

# File activemodel/lib/active_model/type/date_time.rb, line 53
      def mutable? # :nodoc:
        # Time#zone can be mutated by #utc or #localtime
        # However when serializing the time zone will always
        # be coerced and even if the zone was mutated Time instances
        # remain equal, so we don't need to implement `#changed_in_place?`
        true
      end