The `chunk_split()` string function in PHP 8.4 is used to split a string into smaller chunks, inserting a specified separator between each chunk. This is particularly useful when formatting strings such as base64 encoded data to match specific standards like RFC 2045.

Example : Splitting a String into 10-Character Chunks

<?php$text = "The quick brown fox jumps over the lazy dog.";$chunkedText = chunk_split($text, 10, "\n");echo $chunkedText;?>

Output:

The quick brown fox jumps overthe lazy dog.

In this example, the string is divided into chunks of 10 characters each, with a newline character (`"\n"`) inserted after every chunk.