Okay, slimes will now spawn in swamp biomes. Nowhere really said if they had any other requirements beyond low light (>8 (which if I remember correctly, is math for less than eight) )
I built an 8×8 pad 5 blocks down from the skycap in a swamp, verified with f3. It had zero light and enough space for any size to spawn (enough for all but large slimes at the very least). All I had a show up few Endermen. No slimes did.
Any thoughts or ideas? Or better yet any code miners have a great tidbit that I am missing?
I'm using vanilla Minecraft 1.6 prerelease in survival mode without cheats.
P.S. My whole goal is to not have to track down a mythical "slime chunk", but if it should come to that, I already know how, thanks though.
Best Answer
No, slimes can't spawn in the sky.
According to the decompiled Slime Entity code, slimes can spawn in swamps only between the heights of y>50 and y<70. That means a spawning pad 5 blocks below the build limit is far too high-altitude for slimes to spawn.