Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (0,0) content-size 800x125.9375 [BFC] children: not-inline
    BlockContainer <body> at (8,8) content-size 784x109.9375 children: not-inline
      BlockContainer <div.upper> at (8,8) content-size 784x17.46875 children: inline
        line 0 width: 46.15625, height: 17.46875, bottom: 17.46875, baseline: 13.53125
          frag 0 from TextNode start: 0, length: 5, rect: [8,8 46.15625x17.46875]
            "upper"
        TextNode <#text>
      BlockContainer <div.mystery> at (8,100.46875) content-size 784x0 children: not-inline
      BlockContainer <div.lower> at (8,100.46875) content-size 784x17.46875 children: inline
        line 0 width: 43.359375, height: 17.46875, bottom: 17.46875, baseline: 13.53125
          frag 0 from TextNode start: 0, length: 5, rect: [8,100.46875 43.359375x17.46875]
            "lower"
        TextNode <#text>

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x125.9375]
    PaintableWithLines (BlockContainer<BODY>) [8,8 784x109.9375]
      PaintableWithLines (BlockContainer<DIV>.upper) [8,8 784x17.46875]
        TextPaintable (TextNode<#text>)
      PaintableWithLines (BlockContainer<DIV>.mystery) [8,100.46875 784x0]
      PaintableWithLines (BlockContainer<DIV>.lower) [8,100.46875 784x17.46875]
        TextPaintable (TextNode<#text>)
