Does anyone know off the top of their heads how sp

Does anyone know off the top of their heads how special the Special Protocol Request is, or is it something that is often filed with final phase 3 protocol paperwork to the FDA? I like the fact that Leo provided a little insight as to why they are doing it though. So I am hoping that it is in fact an out of the ordinary step, but this is my first rodeo going into a phase 3 trial, and I am still learning. Plus I dont have the time this morning to look it up on the FDA sites. Go CTIX!!