RenderPass appears to write to the "readBuffer"?

In RenderPass.js, why does it write to the readBuffer? It feels to me that either the names are the wrong way around, or some sort of comment would be friendly.

Normally EffectComposer swaps the read and write buffer after a pass. When RenderPass is used, it is usually the first pass in the pass chain. Hence, it’s possible to directly write in the read buffer and safe the swap and the corresponding overhead.