Snes9x.com

I've noticed that Snes9x doesn't recognize any save state dragged & dropped into its window. It gives the error message "unknown file extension", even though the same save state is normally loaded via menu or hotkey.
Dunno whether or not it's a bug, but I'd find it good to be able to do it, since it would compensate for the number limitation (VirtuaNES is a good example of it - the save states are equally limited and numbered, but by dragging & dropping it loads not only the "normal" save states, but also a renamed one).
I guess it'd be a good alternative for the "unlimited save states" featured in emulators such as VBA, Project64 and Dolphin.

do save states include a checksum of the ROM they originate from?

if not, you run the risk of horribly nuking SRAM if you were to load a save state from a different ROM. i'd say then it's not a wise feature to add, since it can lead to data loss.

otherwise, seems reasonable.

I've only tried to do it using a specific game's save states. It'd be senseless to load a state from, let's say, Super Mario World while playing Yoshi's Island, after all, and I'm sure you agree with me at this point.
For example. I'm playing A Link to the Past and I record a .001 save state at some point of the game. This state is perfectly loadable via menu or hotkey, but if I try to drag that very same .001 file and drop it on the emulator's screen, it gives the error message "unknown file extension".

senseless, yes, but quite possible to do by accident.

That's where your previous question takes place. Each save state must have (if they don't already) the respective game's checksum. That way, if one tries to drag & drop a save state from a different game, it'd give an error message like "wrong checksum" or "incompatible checksum", instead of "unknown file extension".