about a regex

[email protected] (Piper H) Sat, 1 Jan 2022 12:21:51 +0800

Newsgroups	perl.beginners
Message-ID	<CA+GLnbh-0wPg=bjb40QdtYJ+b4aQqc-cjB4msaTON-Moh79UfA@mail.gmail.com>

Hello

I know [a-zA-Z0-9] means words and numbers.
But what's the reverse of this regex?

Thank you.

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