I would like to limit visitors to one submission. I know this has to do with cookies and such, but I don't quite know how to do that with WordPress specifically. Basically, I want to set a cookie that checks if the particular user has submitted a form. If so, then a message displays that the form has already been submitted and the form is grayed out (or just not displayed at all). I must not be using the setcookie() function correctly. Is there a specific way that WordPress handles cookies?