0.25 0.4 1 1 1 true 400 300 300 250 0.9

In this example a single teapot is drawn normally while the rest use a material that enables WebGL scissor testing to draw only in the area covered by the floating square. The scissor test area is synced with the square's position using some simple Javascript.

Note: GL state changes aren't part of the XML3D spec, but are available in xml3d.js. See the wiki page for more info.