Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (1,1) content-size 798x120 [BFC] children: not-inline
    BlockContainer <body> at (10,10) content-size 54x102 children: not-inline
      Box <div.flex> at (11,11) content-size 52x100 flex-container(column) [FFC] children: not-inline
        BlockContainer <div.hmm> at (12,12) content-size 50x18 flex-item [BFC] children: inline
          frag 0 from TextNode start: 0, length: 5, rect: [12,12 39.78125x18] baseline: 13.796875
              "Hello"
          TextNode <#text>
        BlockContainer <(anonymous)> (not painted) [BFC] children: inline
          TextNode <#text>

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x122]
    PaintableWithLines (BlockContainer<BODY>) [9,9 56x104]
      PaintableBox (Box<DIV>.flex) [10,10 54x102]
        PaintableWithLines (BlockContainer<DIV>.hmm) [11,11 52x20]
          TextPaintable (TextNode<#text>)
