Document words from nikic

[Danack]

Description

For backwards-compatibility reasons, we'd presumably still have to retain the ability to call those methods on the plain PDO object though :( But at least there would be a way to use it in a sensible way in new code. In particular this also allows you to write things like:

if ($pdo instanceof PDOSqlite) {
    $pdo->loadExtension(...);
}