Design and level pages now have a new screenshot available: the enhanced wireframe. In contrast to the regular wireframe image, this also draws the axis of the arena and its three important boundaries. The axis is the same type of axis on any Cartesian coordinate plan: two lines cross at the origin (0,0). The inner boundary, colored blue, is the immediately viewable area that isn't shrouded by the top toolbar or the sides of the arena. Outside that boundary is the middle boundary, colored red, that is the area that can actually be panned to and viewed. Far out is the outer boundary, colored cyan, that shows the point at which physics "stop." Any object that is wholely beyond this point disappears from the level.
Above is the screenshot from the "Enhanced Wireframe" tab on design and level pages.