Add a uri: psuedo driver; it specifies the name of a resource that contains,
as its first line, the actual data source to connect to.
The resource can be a local file, or it can be any resource for which PHP
has a wrapper.
// loads connection data from the file "myapp"
$d = new PDO('uri:myapp');
// lets say that public.db.com has a read-only db open for the public
// their connection data is also published via the web:
// (not so great to resolve this on each request though...)
$d = new PDO('uri:http://public.db.com/pdo-connection-data');
Still more to come. Give it a couple of days before starting to write drivers
for the other databases; a few things might change, so I'd like to coordinate
that, but in a couple of days.