If it finds [a-z] it's a fail. As simple as that? :)

This setting could work as expected.

I'd be tempted to ignore regex and do the test like this, if it's a possibility you'll have apostrophes, hyphens or similar in your input

e.g. THIS SHOULDN'T FAIL

But this should work as well - only values without any lowercase letters pass

Thanks @danullen, that worked perfectly, keeping it simple :)

Thanks also @ebygomm, that is a much more elegant solution. I love that there are multiple ways to get the same solution.

Thanks @takashi, as always you are a terrific help. I am always impressed by the help provided by the members on this forum.