## 例

`

     string str_rot13 ( string $str )

`

## 説明

Performs the ROT13 encoding on the str argument and returns the resulting string. The ROT13 encoding simply shifts every letter by 13 places in the alphabet while leaving non-alpha characters untouched. Encoding and decoding are done by the same function, passing an encoded string as argument will return the original version.

## 戻り値

Returns the ROT13 version of the given string.