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Only the specifically recognized namespace prefixes are treated as namespaces; anything else is just a regular article with a colon in the title.

This sounds dangerous to me, as people might inadvertantly "pollute" the namespace name space?

But that's just my point: an article titled "E. Coli 0157:H7" or "2001: A Space Odyssey" does NOT create a namespace, so they aren't polluting anything. Only the previously existing namespaces "User", "Talk", "Wikipedia", etc., are treated as namespaces--everything else is just a plain old article, white background, searchable, all that stuff.

There is a concern, I suppose, that it might limit our ability to create real namespaces (and interwiki names) later, in that if we decide to create, say, a "Fred" namespace, any previously existing articles that happen to be named "Fred:..." may have to be changed, but I think a simple convention not to use colons for things other than titles that naturally contain them will minimize that problem, and creating a new namespace is such a major change anyway that having to fix a few article titles won't be much of a problem. 0