Pages tagged reflow:

Stubbornella » Blog Archive » Reflows & Repaints: CSS Performance making your JavaScript slow?
http://www.stubbornella.org/content/2009/03/27/reflows-repaints-css-performance-making-your-javascript-slow/

Going forward the performance community needs to partner more with browser vendors in addition to our more typical black box experiments. Browser makers know what is costly or irrelevant in terms of performance. Opera lists repaint and reflow as one of the three main contributors to sluggish JavaScript, so it definitely seems worth a look.
What causes reflows and repaints. These days usually not a big deal on websites targeted at regular PCs, but could be applicable to mobile devices.
"A repaint occurs when changes are made to an elements skin that changes visibility, but do not affect its layout. Examples of this include outline, visibility, or background color. According to Opera, repaint is expensive because the browser must verify the visibility of all other nodes in the DOM tree. A reflow is even more critical to performance because it involves changes that affect the layout of a portion of the page (or the whole page). Reflow of an element causes the subsequent reflow of all child and ancestor elements as well as any elements following it in the DOM."