Arman

$_SESSION['test'] = isset($_POST['test']) && $_POST['test'];

<?php
$map = [
    1 => 'Jan',
    'Feb',
    // и т.д.
];

echo $map[$month] ?? 'no';
?>

$url = 'https://mysite.com/aaa/bbb/123_multi.jpg';
$searchStr = '_multi';

$parseUrl = parse_url($url);
$pathInfo = pathinfo($parseUrl['path']);

$a = $parseUrl['scheme'] . '://' . $parseUrl['host'] . $pathInfo['dirname'];
$b = $pathInfo['basename'];
$c = (int)(substr($pathInfo['filename'], -strlen($searchStr)) === $searchStr);

$classname = self::getRuleId($requestData, $rules);