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 ** BACKWARD INCOMPATIBILITY **

Since version 2.90, stringification (and string comparison) for
JSON::true and JSON::false has not been overloaded. It shouldn't
matter as long as you treat them as boolean values, but a code that
expects they are stringified as "true" or "false" doesn't work as
you have expected any more.

    if (JSON::true eq 'true') {  # now fails

    print "The result is 1 now."; # => The result is 1 now.

And now these boolean values don't inherit JSON::Boolean, either.
When you need to test a value is a JSON boolean value or not, use
JSON::is_bool function, instead of testing the value inherits
a particular boolean class or not.