When you select and drag a grip, its final position might not be the same as the current cursor position, which might be constrained. For example, for the Lengthen grip on a linear wall, the cursor position is projected to the nearest point on the wall. Whenever the constrained position of a grip differs from the current cursor position, dotted lines or arcs display between the cursor and the grip to indicate how the grip was constrained.
A square-shaped grip typically indicates that the cursor movement is constrained to a plane. An isosceles triangle-shaped grip indicates that the cursor movement is constrained to a line or curve.