Is this true? I've never seen this mentioned anywhere, and some googling doesn't show me any mention of this. Do you have a reference to something that verifies

Is this true? I've never seen this mentioned anywhere, and some googling doesn't show me any mention of this. Do you have a reference to something that verifies this and/or explains it? I can totally understand how CSS expressions would be re-evaluated due to a repaint (resizing the window, manipulating DOM elements with javascript, etc)... but it doesn't make any sense that simply moving your mouse would cause this.