Thought it was better if it qualified the word "subject" to explain it as a `RACPropertySubject` that observes something, rather than a `RACSubject` that has something to do with observable properties, because that would imply `RACPropertySubject` has something to do with non-observable (or both observable and non-observable) properties.

It did end up a bit awkward sounding though, so I changed it to what you proposed.