Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (0,0) content-size 800x0 [BFC] children: not-inline
    Box <body> at (8,8) content-size 50x50 positioned flex-container(row) [FFC] children: not-inline
      ImageBox <img> at (8,8) content-size 50x50 flex-item children: not-inline

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x0]
    PaintableBox (Box<BODY>) [8,8 50x50]
      ImagePaintable (ImageBox<IMG>) [8,8 50x50]
