这个'isset（$ _ POST）'代码在做什么？

Question

Trying to understand what this isset($_POST) code is doing

if (isset($_POST['Submit'])) {
    $title=$_POST['title'];
    $forename = $_POST['forename']; 
    $surname=$_POST['surname'];
    $dob=$_POST['dob'];
    $gender=$_POST['gender'];
    $email=$_POST['email']; 
    $phone=$_POST['phone'];
    $password=$_POST['password'];


    if (authRegister($title, $forename, $surname, $dob, $gender, $email, $phone, $password))
    {
        echo 'Thank you for registering your details, you can now login';           
    } 
    else
    {
        outputErrors();
    }

Answer 1

It checks that there is a field with name 'Submit' (probably submit button) in the form submitted to this php page. In other words it shows that for has been submitted and has to be processed.

In addition I'll say that whenever you post form to a php page all fields that have name attribute of the form are represented in the $_POST array. There is 2 ways to check if a key exists in an array:

$array = array('key_name' => 'value');
isset($array['key_name']);
array_key_exists('key_name', $array)

isset() also returns false if the 'key_name' exists in $array but value is null. array_key_exists would return true in this key.