Retrieving flattened XML from straight HTTP request

We have Arbortext Publishing Engine, and are looking to retrieve a complete, flattened XML document for a given Object ID by way of a straight HTTP request (not SOAP).

Where can we find sample code / documentation?  We'll be using PHP, but examples in any language would do -- or, if there was documentation about how to construct the URL, that would be great too.

Much Appreciated!