$breaks = '[^\w\x80-\xff]';
// regexp for roman numbers
- $roman = 'M{0,4}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})';
+ // Lookahead assertion ensures $roman doesn't match the empty string
+ $roman = '(?=[MDCLXVI])M{0,4}(C[DM]|D?C{0,3})(X[LC]|L?X{0,3})(I[VX]|V?I{0,3})';
$reg = '/^' . $roman . '$|^' . $roman . $breaks . '|' . $breaks
. $roman . '$|' . $breaks . $roman . $breaks . '/';