In contenteditable div, The line-break made by pressing the enter key is indeed shown as a new line in this div. But when the value of the div being posted and fetched, the line break doesn't show up. I think by default it is captured as an empty string when posting to database and fetch out. I wondered what is the most common way to make it posted and fetched as a line break?
Pass your text through nl2br before displaying it. It will transform new line breaks into <br> tags.
$value = nl2br("Your
data");
?>
<div><?php echo $value;?></div>