&reftitle.constants; &extension.constants; MB_OVERLOAD_MAIL (integer) MB_OVERLOAD_STRING (integer) MB_OVERLOAD_REGEX (integer) MB_CASE_UPPER (integer) MB_CASE_LOWER (integer) MB_CASE_TITLE (integer) MB_CASE_FOLD (integer) Available since PHP 7.3. MB_CASE_LOWER_SIMPLE (integer) Available since PHP 7.3. MB_CASE_TITLE_SIMPLE (integer) Available since PHP 7.3. MB_CASE_FOLD_SIMPLE (integer) Used by case-insensitive operations. Available since PHP 7.3.