For my sliding door drapery panel, I have my sections of face fabric sewn together and will be attaching the interlining (flannel) next.

Originally, I was planning to just baste stitch the interlining to the perimeter of the piece. The more I thought about this, the more concerned I became about the flannel drooping once the drape is hung. So...I consulted a book which recommends:

Lock the interlining to the main fabric by lockstitching (by hand) all the way down each seam and twice between each seam.

Is the locking twice between seams just a stationary stitch?

Sounds like this will be worth it in the long run, but gosh, it tires me just thinking about it.