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I have a few questions regarding the update from version 1.21 to 1.22. There are many new updates in 1.22. If I update my current 1.21 world to 1.22 and run it, will it automatically change to fit the 1.22 version? Also, are there any parts that might not apply properly after the change? Will the areas I’ve already played in remain exactly as they are, with the new features applying only to newly discovered areas? Regarding the new dungeon system, do I have to travel all the way to a new region to find them, or will they be added to existing areas as well? Are there any specific "issues" or circumstances that would make it better to just start a completely new world? I’ve played this world for 200 hours and would hate to lose it, so would it be okay to just keep going with this world without any major problems? Also, is there perhaps an existing post or guide that summarizes these concerns?

Can't I place two slabs in a single block space—one on the left and one on the right—to create one block shape? I want the exterior to be a stone slab and the interior to be a wooden slab, so it looks like a stone house from the outside and a wooden house from the inside. If that's not possible, is it intended to be that way? Or is there a specific reason why it’s not supported?