"on bottom" = same coordinate system as on top, but stay below all application windows. I think it's sensible to have a simple, intuitive term for this effect. Whether or not the code literally works that way shouldn't really matter if you ask me. :)

Just docking to the desktop will break systems with extra monitors in negative space. Well, unless everyone messing with module positions is intimately aware of how the desktop window works, how docking works, and how multimonitor coordinates work. (with no motivation, I might add, since the vast majority of themers have only one monitor)

Ok, probably a small issue for most people, but when it comes to breaking horribly for a small percentage of people vs. working perfectly for everyone, I'll go for working perfectly. :)