The interior flanges...
...are folded in half and stitched...
...and one side of the zipper...
...is pinned to each of them.
(It's easy to shorten a 'too-long' zipper using strong nylon thread...
...just stitch across the teeth several times...
...at the desired spot.)
Machine stitching the zipper into place.
The addition of an interior flange...
...allows for a wider opening...
...at the mouth of the bag...
...and avoids 'visible stitching lines'...
...on the bag surface.
