You can tag arbitrary content on the web, you can do it in a low-tech way to make it easy for everyone to do...But...How do you find instances that people haven't tagged? Or deal with overlapping meme labels?
In general, a namespace is an abstract container providing context for the items (names, or technical terms, or words) it holds and allows disambiguation of items having the same name...As a rule, names in a namespace cannot have more than one meaning, th