Final answer:
The setcookie() function must be called before the tag, since it sends an HTTP header that needs to be set before any webpage content is sent.
Step-by-step explanation:
The setcookie() function in PHP should be used before the <html> tag. This is because the setcookie() function is used to send a raw HTTP header to the browser, and according to the HTTP protocol, headers must be sent before any actual content. This means that setcookie() needs to be called before the webpage starts to output any HTML code to ensure that the cookie is properly set. If you attempt to call setcookie() after content has been sent to the browser, PHP will not be able to send the cookie header and it will result in an error.