19RSD Dinette/Bed Question

Hi All.

I was hoping someone could answer a question about the dinette on the 19RSD. Unfortunately I haven't been able to see one in person yet and have seen some mention that the dinette turns into a bed to allow a 5th person to sleep. How does this work? I haven't seen a picture of it in bed formation and it has me a bit puzzled. I can see in a few pictures that it looks like the side of the bottom bunk may have a rail on it, but a description or picture would really help me out!

Thanks!