Found it. It refers to a special technique in Diagram 1 on page 96. There is not a diagram 1 on that page. Nothing on page 96 is about setting in a partial seam. It's the last steps in how to make a Quillow. I think it is referring to diagram 1 on page 52. It's the only thing that makes sense. I think the pattern Weaver Fever is the same thing but less complicated.