Represents a navigation element on the second level of the TileNavPane navigation hierarchy.
The TileNavPane is a hierarchical control. Each hierarchy level is rendered as a tile bar, in which elements are represented as tiles. The top hierarchy level is a bar displaying categories (TileNavCategory) as tiles. The second hierarchy level is a bar displaying items (TileNavItem) as tiles. And the last hierarchy level is a bar displaying sub-items (TileNavSubItems) as tiles.