In an extremely strict covering family, what is the smallest eye-opening that is common and what is the usual amount of eye-screening layers (veils dropped down to cover the opening and/or mesh screening as in the burqa). One sees pictures such as the above, but could it be that there is a mesh inside of the mesh to conceal the eyes (and the world to the wearer) more? If there is no size of opening average, would an opening reduced to little more than a crack be acceptable?