The first step in weaving is to stretch the warp, or longitudinal, yarns, which must be very strong. The weft, woof, or filling crosses the warp, binding the warp threads at either side to form the selvage. The three essential steps after the warp is stretched are: shedding, or raising every alternate warp yarn or set of yarns to receive the weft; picking, or inserting the weft; and battening, or pressing home the weft to make the fabric compact. In most primitive weaving these operations were performed by the hands alone, as in making rush mats and baskets. Gradually frames for holding the warp evenly stretched and devices for throwing the weft came into use (see loom).