&warn.deprecated.feature-7-2-0; You might often find it difficult to get an existing PHP application to work in a given multibyte environment. This happens because most PHP applications out there are written with the standard string functions such as substr, which are known to not properly handle multibyte-encoded strings. mbstring supports a 'function overloading' feature which enables you to add multibyte awareness to such an application without code modification by overloading multibyte counterparts on the standard string functions. For example, mb_substr is called instead of substr if function overloading is enabled. This feature makes it easy to port applications that only support single-byte encodings to a multibyte environment in many cases. To use function overloading, set mbstring.func_overload in &php.ini; to a positive value that represents a combination of bitmasks specifying the categories of functions to be overloaded. It should be set to 1 to overload the mail function. 2 for string functions, 4 for regular expression functions. For example, if it is set to 7, mail, strings and regular expression functions will be overloaded. The list of overloaded functions are shown below. value of mbstring.func_overload original function overloaded function 1 mail mb_send_mail 2 strlen mb_strlen 2 strpos mb_strpos 2 strrpos mb_strrpos 2 substr mb_substr 2 strtolower mb_strtolower 2 strtoupper mb_strtoupper 2 stripos mb_stripos 2 strripos mb_strripos 2 strstr mb_strstr 2 stristr mb_stristr 2 strrchr mb_strrchr 2 substr_count mb_substr_count 4 ereg mb_ereg 4 eregi mb_eregi 4 ereg_replace mb_ereg_replace 4 eregi_replace mb_eregi_replace 4 split mb_split It is not recommended to use the function overloading option in the per-directory context, because it's not confirmed yet to be stable enough in a production environment and may lead to undefined behaviour.