PHP form validation

Question:

Standard introduction : I'm just starting to learn php, don't swear for a stupid question, etc. Code from the book by Robin Nixon.

<?php
if (isset($_POST['name'])) $name = $_POST['name'];
else $name = '(Не введено)';
echo <<<_END
<html>
    <head>
        <title>Test</title>
    </head>
    <body>
    Вас зовут $name<br />
    <form method = 'post' action = 'count.php'>
        Как вас зовут?
        <input type='text' name='name' />
        <input type='submit' />
    </form>
    </body>
</html>
_END
?>

Question: In the second line, using isset (), we check whether the variable is set or not. In the third, we have a condition: if it is not set, then we display "(Not entered)". Here's what I don’t understand: I open the page – displays:

Your name is (Not entered) What is your name? (and a form to submit)

I do not enter anything, I press "send" – it displays:

Your name is What is your name? (and does NOT output "not entered") (and the form to submit)

That is, I do not enter anything, but the function considers that the variable was set to a value other than NULL . Why? If it misses a null value, then why use it? Why not use empty ? But in all programs I see just such a check. What do I not understand?

Answer:

Yes, after the submission $ _POST ['name'] got the right to exist ( isset ).
After all, an empty string is also a value.
And if there is a value, then there is a variable.
But as you pointed out, why not take empty ?
The difference is that empty checks the value of an existing variable for emptiness.
Therefore, a double condition would be optimal here:

if (isset($_POST['name']) && !empty($_POST['name']))
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