You Can Use The htmlentities
<?php
$comments = "A 'quote' is <b>bold</b>";
echo "<textarea>".htmlentities($comments )."</textarea>";
?>
DEMO:: http://phpfiddle.org/main/code/n0sf-b7ka
You Can Also Do This.
if (isset($_POST["submit"]) && !empty($_POST["comments"])) {
$comments = $_POST["comments"];
echo "<textarea>".htmlentities( $comments )."</textarea>";
}
solved Prevent tags being used in