Are nested forms allowed in PHP, and what potential pitfalls should be considered when using them?

Nested forms are not allowed in HTML, and therefore not in PHP either. When attempting to use nested forms, the browser can behave unpredictably and may not submit the data as expected. To work around this limitation, consider restructuring your forms to be separate and independent of each other.

```php
<!-- Incorrect nested forms -->
<form action="process1.php" method="post">
    <input type="text" name="field1">
    <form action="process2.php" method="post">
        <input type="text" name="field2">
        <input type="submit" value="Submit">
    </form>
    <input type="submit" value="Submit">
</form>
```

It is not recommended to use nested forms in PHP. Instead, consider restructuring your forms to be separate and independent of each other.