Advice on how to implement area conditioning

I'm a big fan of ComfyUI's "area condition" technique and I really want to figure out how to implement it.

I've been looking through ComfyUI's source code but I can't seem to figure out where exactly the conditioning actually gets applied (or rather just comes into play, I'm not sure of the terminology). I'm just not sure what shape of a tensor conditioning actually is. Is it just a 1d vector? An nd tensor? Where does the values of conditioning come from and where do they come into play? Before/during the sampling process?

Any help or advice on this would be appreciated.