[php] Preg_match backtrack error

When I use the regex (.*)*[0] everything works well:

preg_match('/(.*)*[0]/', 'this is a test string'); var_dump(preg_last_error()); // no code's returned 

But when I add another character to char class, it will throw out error:

preg_match('/(.*)*[01]/', 'this is a test string'); var_dump(preg_last_error()); // int(2) 

Code #2 means PREG_BACKTRACK_LIMIT_ERROR. What an additional character can do here though?

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