How can hidden fields be used in PHP forms to pass information for validation purposes?

Hidden fields can be used in PHP forms to pass information for validation purposes by including them in the form but making them hidden so that users cannot see or modify them. This can be useful for passing information such as user IDs or timestamps that are needed for validation but should not be visible or editable by users. 

```php
<form method="post" action="process_form.php">
    <input type="hidden" name="user_id" value="<?php echo $user_id; ?>">
    <!-- Other form fields here -->
    <input type="submit" value="Submit">
</form>
```

In the above code snippet, a hidden input field named "user_id" is included in the form with the value of the $user_id variable. This information can then be passed to the processing script for validation without being visible or editable by the user.

Keywords

hidden fields PHP forms validation information passing technical keywords

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