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<?php setlocale( LC_ALL, 'C'); var_dump( preg_match( '`^\w+$`u', 'Iñtërnâtiônàlizætiøn' ) );
based on eJVTY
Output for 5.3.4 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.30, 7.0.0 - 7.0.30, 7.1.0 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.28, 7.4.0 - 7.4.16, 8.0.0 - 8.0.3
int(1)
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.3
int(0)