Despite all more-or-less-complicated suggestions regarding this topic, I'd like to repeat an idea I mentioned once as a compromise on subpages. It was rejected by Larry at that time, but it might be worth thinking about it again in the light of the [[Middle Earth]] issue.
The idea: On saving an edit, all links that start with "[[/" (like [[/Frodo]] on the [[Middle Earth]] page) would be extended by the "root" topic (like [[Middle Earth/Frodo]]).
That would give us back just a little subspace functionality, but would keep the system "clean" (no automatic backlinks, no weird stuff on "GNU/Linux" etc.). It just saves some typing. Personally, I doubt that would encourage massive wild-growth of subpages, but of course, I'll accept the decision of the powers-that-be ;)
Magnus
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