Reflow is the process by which the geometry of the layout engine’s formatting objects are computed. The HTML formatting objects are called frames: a frame corresponds to the geometric information for (roughly) a single element in the content model; the frames are arranged into a hierarchy that parallels the containment hierarchy in the content model. A frame is rectangular, with width, height, and an offset from the parent frame that contains it. (Izvor: Mozilla)
It is an interesting visualization technique of browser’s page arrangement. Unfortunately, I don’t know how it is done and is there available aplication that uses this technique, but videos I have found are more that intersting, must see!
Reflow mozilla.org:
Wikipedia:
Google:
(via Reddit)