I recently ran across a term in some old articles on tailoring called a "tailor's blister."   It's used on notched collars when attaching the facing/upper collar to the under collar and helps to get lapels and collars on blazers to lay flat.   It seems like a useful concept, but I can't find any reference to the term and so how to make one.  Is anyone familiar with a tailor's blister and how to make one?