Returns the receiving buffer after overlaying it, starting at the n'th character, with the string new, padded or truncated to length length. The overlay can extend beyond the end of the buffer. In this case the buffer size will be increased. If you specify length, it must be a positive integer or zero. The default value for length is the length of new. If n is greater than the length of the buffer content, padding is added before the new string. The default pad character is a blank, and the default value for n is 1. If you specify n, it must be a positive integer.