Is there a difference when using brackets in include & require?

Question

When using include/include_once and require/require_once, the PHP docs show examples as such:

include 'filename.php';

And also on the same page, users have contributed examples looking like this:

include ('filename.php');

As far as I can see, the PHP docs do not mention the required use of brackets, or even any ability to include them. Do the brackets make a difference to how the function works?