In knitting, ribbing is formed of alternating vertical courses of knit and purl stitches. When unstretched, the resulting fabric naturally contracts, with purl stitches receding and knit stitches standing out. Ribbing may be composed of equal numbers of knit and purl stitches (eg k1 p1, k2 p2) or unequal numbers of knit and purl stitches (eg k2 p1, k3 p2). Ribbing makes a fabric that does not curl and for that reason is often used at the edges of garments.