Source: THOMAS, Mary (1934). Mary Thomas's Dictionary of Embroidery Stitches, London: Hodder and Stoughton, p. 26.
GVE
The double buttonhole stitch is an embroidery technique consisting of two rows of buttonhole stitches or blanket stitches. A row of stitches are worked leaving a space between each stitch and then the work is turned around 180 degrees and another row of stitches is worked, making sure that the stitches of the second row fit into the spaces left by the first. Sometimes another thread or a ribbon is threaded through the stitches.
Source: THOMAS, Mary (1934). Mary Thomas's Dictionary of Embroidery Stitches, London: Hodder and Stoughton, p. 26.
GVE