CURL proxy issue

Anyone knowing why curl successfully uses socks5 and prints an error on socks4?

This works:

curl_setopt($ch, CURLOPT_PROXYTYPE, CURLPROXY_SOCKS5);

PHP:

This doesn't:

curl_setopt($ch, CURLOPT_PROXYTYPE, CURLPROXY_SOCKS4);

PHP:

The error:

Notice:  Use of undefined constant CURLPROXY_SOCKS4 - assumed 'CURLPROXY_SOCKS4'

Code (markup):

 

Like the error already says, it's because that constant is not defined and php curl probably doesn't support socks 4 proxies.

http://www.php.net/manual/en/curl.constants.php