How can error messages be correctly displayed in a PHP login form design?

To correctly display error messages in a PHP login form design, you can use session variables to store and show error messages when needed. This allows you to provide feedback to users when they enter incorrect credentials or encounter other issues during the login process.

// Start the session
session_start();

// Check for errors and display them
if(isset($_SESSION['error'])){
    echo '<div class="error">' . $_SESSION['error'] . '</div>';
    unset($_SESSION['error']);
}

// Example of setting an error message
$_SESSION['error'] = "Invalid username or password.";