(PHP 5 >= 5.2.0, PECL zip >= 1.4.0)
ZipArchive::setArchiveComment — Set the comment of a ZIP archive
$comment
   )Set the comment of a ZIP archive.
commentThe contents of the comment.
   Returns TRUE on success or FALSE on failure.
  
Example #1 Create an archive and set a comment
<?php
$zip = new ZipArchive;
$res = $zip->open('test.zip', ZipArchive::CREATE);
if ($res === TRUE) {
    $zip->addFromString('test.txt', 'file content goes here');
    $zip->setArchiveComment('new archive comment');
    $zip->close();
    echo 'ok';
} else {
    echo 'failed';
}
?>