Syntax of chunk_split in PHP
string chunk_split(string string[, int size[, string postfix]])
Inserts postfix into string after every size characters and at the end of the string; returns the resulting string. If not specified, postfix defaults to \r\n and size defaults to 76. This function is most useful for encoding data to the RPF 2045 standard
Example of chunk_split
<?php
// format $data using RFC 2045 semantics
$new_string = chunk_split(base64_encode($data));
?>