获取此示例中的按钮值[关闭]

Does anyone knows here how they did this? http://www.w3schools.com/tags/tryit.asp?filename=tryhtml_button_value2. Unfortunately, it is not part of their tutorial. Sorry for the question , I am just a beginner and I want to understand these things. Thank you.

There are numerous tutorials out there ... This could be as simple as:

<?php if(isset($_GET['subject'])): ?>
    <?= 'You chose: ' . $_GET['subject']; ?>
<?php else: ?>
<html>
    <body>
        <form method="get" action="<?= $_SERVER['PHP_SELF']; ?>">
            Choose your favorite subject:
            <button type="submit" name="subject" value="fav_HTML">HTML</button>
            <button type="submit" name="subject" value="fav_CSS">CSS</button>
        </form>
    </body>
</html>
<?php endif; ?>