For those who don't know Haapsalu shawls at all, they are a traditional Estonian lace shawl type. Most commonly they are rectangular stole-shaped, though they can be square or triangular. They are traditionally quite lacy, knit with very fine wool yarns in natural colors, and they almost always feature a sawtoothed edging. This adds both beauty and practicality; it is much easier to block a shawl by pinning out points at the ends or better yet all around than it is to block out straight edges.
Historically the stoles were knit end-to-end, the edgings were knit in long straight strips (two long strips, each to be matched to two contiguous sides of the shawl); and then the edgings were sewn onto the main body of the shawls. Today with our modern flexible, long circular needles it has become possible and popular instead to pick up stitches around the edges of the main shawl body and work outward.
The traditional method allows simple paired or centered decreases and yarn overs to easily form the typical chevrons within just a few rows. You'll be able to see it when you knit your socks by the time you finish the first round of the lace chart; there will already be peaks where the centered decreases occur and valleys in between them. This effect will become more pronounced as you work the first few rows. The down-side of the traditional method is that it is not uncommon to have to cast on 800-1000 stitches for each edging half, and then hope that you don't miscount all those stitches nor the first row of lace patterning. One mistake and you often must tear the whole thing out and start the edging over. Once the first row or two of lace is established, though, it's usually very easy to read where you are in the repetitive patterns and immediately identify and fix any future mistakes.
Aflight uses a very traditional, old-fashioned, simple Haapsalu-type edging. You cast on (in Haapsalu shawls knit in fine lace yarns, often this would be done with two yarn strands, the second one dropped when the cast-on is completed); work a couple of rows to create a strong and stable edge, then begin the simple 10-stitch-repeat lace pattern. Since we are only working 70 stitches in a round, and that is broken up into two parts, it is much easier to note if you get off-count in the first round.
For variation, if you like or if you knit a second (or third, or fourth) pair using this pattern, you could elongate the lace by repeating rounds 17-20 as many times as you like before going on to rounds 21 and 22.
You could also add nupps, Estonian bobbles, on the sixth stitch of each repeat on rounds 9, 11, 13, and or 17. To work a nupp in stitch #6, work (K1, yo, K1, yo, K1, yo, K1) in that stitch before working the next stitch. You have made 1 stitch into a knot of 7 strands of stitches (you can work 3 or 5 or even 9 strand nupps if you prefer, but I find the 7-strand version the most visually pleasing in fingering weight sock yarn). On the following round, when you reach that bobbled stitch, knit all the strands together through the back loop (if you were working flat you would simply purl them together; when working in the round, knitting them all tbl best forces the nupp to show to best advantage on the right side of the work). You are back to a single stitch. Haapsalu shawl knitters favored adding nupps to their work because nupps cannot be worked on knitting machines; they are a guarantee that any piece with nupps in the patterning was hand-knit. In addition, they add beauty and structural interest.
For further reading, please consider:
The Haapsalu Shawl: a knitted lace tradition from Estonia, by Siiri Reimann, 2011
Knitted Lace of Estonia: techniques, patterns and traditions, by Nancy Bush, 2008