Future developers may want to clean up some code after bumping required versions, so explicitly state that JSON_UNESCAPED_SLASHES was introduced in PHP 5.4.0 and that the PHP JSON extension is a core PHP extension since PHP 8.0.0 and cannot be disabled anymore, to save time looking up stuff.
https://www.php.net/ChangeLog-5.php#5.4.0
https://www.php.net/manual/en/json.installation.php