Sticky headers and nav bars pin while you scroll

The most common thing that made real pages feel wrong in Floati's from-scratch engine is fixed: sticky page furniture now stays put while you scroll. A navigation bar, a section heading, a toolbar or a table's header row that a site marks to stick now pins to the top of the window as you scroll past it, holds its place while the article moves underneath, and lets go again at the bottom of the section it belongs to - exactly the way it behaves in the reference browser. Until now these elements simply scrolled away with the rest of the page, which broke the feel of almost every modern site. Doing it properly meant keeping a pinned element in place without repainting the whole page on every scroll, so long pages still scroll smoothly. It works today on Windows and on non-retina Macs; the same behaviour on retina Mac displays follows in a coming update. The layout grade stays at ninety-nine - the last point still waits on right-to-left text for Arabic and Hebrew and a few print-oriented features.