rear wall and or a top wall are possible without deviating from the scope of the invention the right hand and left hand end structures to this end may be modified to provide additional engagement formations for receiving such rear and or top walls where the blind is a roller blind the bottom wall is usually arranged to leave a longitudinal slot along its longitudinal rear edge to allow the blind fabric or screen material to extend from the head rail in proximity to the rear of the head rail occasionally it is preferred to have the blind or screen material to extend in proximity of the front wall of the head rail in such cases the bottom wall can be formed as an integral part of a rear wall or be separately attachable to the left hand and right hand end structures because the front wall of the head rail assembly can sometimes have an additional decorative function it goes without saying that this does not strictly need to have a flat shape and can be curved or profiled according to requirement the invention is not limited to any embodiment herein described and within the purview of the skilled person modifications are possible which should be considered within the scope of the appended claims equally all kinematic inversions are considered inherently disclosed and to be within the.