Description:
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Docs available at https://github.com/kkos/oniguruma/blob/master/doc/RE. None on php.net for mbstring. The PCRE docs at https://secure.php.net/manual/en/regexp.reference.character-classes.php are not relevant for mbstring onigunuma.

Test script:
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N/A

Expected result:
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Documentation exists for mbstring/oniguruma regex patterns

Actual result:
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No documentation exists