This example will check which features are available in the cURL build by using the 'features' bitmask returned by curl_version.

<?php
// Get curl version array
$version = curl_version();

// These are the bitfields that can be used 
// to check for features in the curl build
$bitfields = Array(
            'CURL_VERSION_IPV6', 
            'CURL_VERSION_KERBEROS4', 
            'CURL_VERSION_SSL', 
            'CURL_VERSION_LIBZ'
            );


foreach($bitfields as $feature)
{
    echo $feature . ($version['features'] & constant($feature) ? ' matches' : ' does not match');
    echo PHP_EOL;
}
?>