@thisisaaronland @Edent tight.
Another question: since they both match the pattern something:other=third how can I tell that the first example is an URL and the second example is a machine tag?
(1) https://google.com/search?q=machine+tag
(2) dc:topic="machine tags"
I think the first is not a machine tag because of the "/" and "?" and "." characters. I think it's probably a good rule of thumb to avoid the most common URL protocols (http, https, ftp, ...) as a namespace.