To quote perlre

The "*" quantifier is equivalent to "{0,}", the "+" quantifier to "{1,}", and the "?" quantifier to "{0,1}". n and m are limited to integral values less than a preset limit defined when perl is built. This is usually 32766 on the most common platforms. The actual limit can be seen in the error message generated by code such as this:

           $_ **= $_ , / {$_} / for 2 .. 42;
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Searching in perlre for "limit" and stepping to the third hit revealed that.