Immediately after the post you quoted, Nevcairiel answered the question in great detail, with multiple example code snippets. If there was some part of his answer you didn't understand, please be more specific about what question(s) you still have.
off-topic, but can we also just link to e.g. the online FrameXML browsers/repositories in our XML files
No. I don't think WoW even cares about the xmlns attribute (I've seen plenty of addons that don't include it but do, presumably, work just fine), but if it does, Blizzard certainly would not let you point it to random third-party URLs.