Why a TileScheduler wants a tile, in the order it renders them.
public enum TilePriority
Spec #33 viewer capability 3: visible first, then near the viewport, then ahead in the scroll direction.
kind:method, kind:property, kind:ctor. Press Esc to clear.AheadIt lies ahead in the scroll direction, within RenderAhead viewports.NearIt lies within NearMargin of the viewport.VisibleThe viewport shows it: a visible page's placeholder, then its sharp tiles.