I've been browsing the documentation relentlessly, but I just can't seem to figure out what it's called when a function uses an argument which has an int datatype. For example, in filter_var:
filter_var('bob@example.com', FILTER_VALIDATE_EMAIL);
... or in curl
curl_setopt($curl, CURLOPT_URL, 'http://example.com');
What is FILTER_VALIDATE_EMAIL and CURLOPT_URL called?