Add a part to a multipart body.
<?php
$multi = new http\Message\Body;
$multi->addPart(new http\Message("Content-type: text/plain\n\nHello part 1!"));
$multi->addPart(new http\Message("Content-type: text/plain\n\nHello part 2!"));
echo $multi;
?>
Yields:
--8a72b190.3fe908df
Content-Type: text/plain
Content-Length: 13
Hello part 1!
--8a72b190.3fe908df
Content-Type: text/plain
Content-Length: 13
Hello part 2!
--8a72b190.3fe908df--