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Oh boy what a beautiful regex. I'm sure it does something logical and easy to understand.
(lemmy.world)
^.?$|^(..+?)\1+$
Matches strings of any character repeated a non-prime number of times
I thought, the +? was going to be a syntax error. ๐
I was like, why specify "one or more" and then make it optional? Isn't that just .*?