The detached buttonhole stitch is formed in the same way as the buttonhole stitch but it is worked into itself rather than into the foundation fabric.
To start, outline the surface to embroider with back stitches to attach your rows of buttonhole stitch. Working from left to right, work a row of buttonhole stitches over the top back stitches without entering the foundation fabric. Snake through the vertical back stitch at the end of the row. Now, work from right to left in the same way. The second and subsequent rows are anchored in the loops between the stitches.