What kind of method is the 'lip buttonhole' mentioned in the jacket description?

A lip buttonhole refers to a finishing method that neatens the opening by adding thin borders above and below, resembling lips. It is also called a bound buttonhole because the edge of the hole is bound with fabric. While regular buttonholes are made by slitting the fabric and densely stitching around it with thread, a lip finish delicately binds and stitches the same leather or cloth as the outer fabric inside and out around the opening. Because the sewing threads do not protrude outward, the surface remains sleek and neat.

Moia's dolman leather jacket is a cropped jacket made of Italian vegetable lambskin^[1][2]. The front features a one-button structure fastened with just a single button, pairing a nut button engraved with the logo precisely with this lip buttonhole^[3].

The buttonhole area, frequently touched by hands, experiences strain each time the button is fastened and unfastened. If soft and flexible lambskin is finished only with thread, the circumference of the hole can easily stretch out or the cut edge of the leather can become damaged. Wrapping and sewing the mouth of the opening once more with a leather border creates the strength to withstand friction, and even when the button is fastened, the opening gap does not spread apart and closes neatly like a single line.