I think the author means "I said everything is immutable, and rebinding is obviously changing something, but the thing it changes doesn't count!". The idea bein

I think the author means "I said everything is immutable, and rebinding is obviously changing something, but the thing it changes doesn't count!". The idea being, if you read a bunch of code, none of the variables in that piece of code can have the value of it changed unless there is some explicit line of code.