It is possible to attach a plate (or tile) to the underside of a
square rectangular brick/plate/tile, between the wall and the tubes, like so:
Note how the distance between a brick's wall and its inner tube seems to be the same as the thickness of a plate:
A few observations:
This connection feels looser (seems to have less clutch) than using a round brick.
For 1-stud-wide plates, this connection doesn't guarantee a straight angle. The edge of the plate sits loose inside the brick.
For post-2005 regular bricks (i.e. non-sloped), since they have thinned walls with notches at every stud, the connection is particularly flimsy. A 1-stud-wide plate just won't get any grip at all.
The walls of rectangular bricks are connected to each other, so bending a wall "outwards" (to jam a plate/tile inside) means bending or stressing the perpendicular walls (as far as I understand the physics of solid materials).
Is this connection "legal"? (i.e.: Does this connection stress the parts involved?)
Has this type of connection been used in any official sets?