What best practices should be followed when handling form data in PHP, particularly when dealing with checkboxes and unset values?

When handling form data in PHP, particularly checkboxes, it's important to handle unset values properly to avoid errors. One way to do this is by using the isset() function to check if a checkbox value is set before trying to access it. If the checkbox is unchecked, it will not be included in the form data, so checking if it is set will prevent errors when trying to access its value.

// Check if the checkbox is set before accessing its value
$checkbox_value = isset($_POST['checkbox_name']) ? $_POST['checkbox_name'] : '';