And that, of course, is one reason that these discussions get so heated: different definitions and people talking about totally different questions.

If the definition of sandbox is: "Every player is part of one server, one scene, one storyline" -- and that's it -- then a great many people read a lot of "and" into the definition, so that "sandbox" becomes their version of what it should be.

If we accept the above definition, then Perpetuum is a sandbox game essentially because it has everyone playing in the same world, period.  The various gameplay mechanics, types of play, set-up of islands, etc., may contribute to the "feeling of being in a sandbox", but are not part of the definition.

So, what we are really taking about seems to be: what toys do we wish to play with in the sandbox?  And do we need to worry about making the sandbox inviting enough to attract people that like different toys, or do we cater to a narrower selection in favour of certain types of play?  If we want to play with blocks, do we want people in the box that would rather play with action figures?  Or dump trucks?  Or do we shoo them away, to keep our low-population blocks game "pure"?