So those first efforts were all about making that license descriptor less fragile and easier to discover.
The Validator fetched a URI, parsed the source, and tried to find the comment. If it found it, it tried to parse it as RDF, and then match the license information. Any parsing errors were spit back to the user.
mozCC did something similar, albeit with the current page in the browser. It ran on pretty much every page, and when it found the license, it displayed an icon in the status bar.