Motif fills are similar to regular fills. You control the density and gradient. Motif fills can be curved as with regular fills. In motif fills, the traveling stitches always run along the edge so as not to interfere with the motifs. The motifs are added in the same manner as motif runs.
The density adjustment in motif fills adjusts spacing between each line in the fill. A zero value here will cause each row to just touch the previous row.
Please see the Motif Run section for details on the use of motif controls.