Why in the names of variables in the code of some engines in the names of classes they write small letters first?

Question

OOP

Why do they do this in class names: a ClassSome, with OtherClass, o LoginClass, and so on? (class names outlined abstractly).
Example:

require_once($sPathToFramework . '/bootstrap/start.php');
/**
 * Подключаем загрузчик конфигов
 */
require_once($sPathToFramework . '/config/loader.php');
/**
 * Определяем дополнительные параметры роутинга
 */
$aRouterParams = array(
    'callback_after_parse_url' => array(
        function () {

Answer 1

I think this should help
Hungarian notation