Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (0,0) content-size 800x600 [BFC] children: not-inline
    BlockContainer <body> at (8,8) content-size 784x34 children: not-inline
      BlockContainer <(anonymous)> at (8,8) content-size 784x0 children: inline
        InlineNode <details>
      ListItemBox <summary> at (32,8) content-size 760x17 children: inline
        frag 0 from TextNode start: 0, length: 13, rect: [32,8 114.625x17] baseline: 13.296875
            "I'm a summary"
        TextNode <#text>
        ListItemMarkerBox <(anonymous)> at (8,8) content-size 12x17 children: not-inline
      BlockContainer <slot> at (8,25) content-size 784x17 children: inline
        TextNode <#text>
        TextNode <#text>
        InlineNode <span>
          frag 0 from TextNode start: 0, length: 10, rect: [8,25 82.3125x17] baseline: 13.296875
              "I'm a node"
          TextNode <#text>
        TextNode <#text>
      BlockContainer <(anonymous)> at (8,42) content-size 784x0 children: inline
        TextNode <#text>

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x600]
    PaintableWithLines (BlockContainer<BODY>) [8,8 784x34]
      PaintableWithLines (BlockContainer(anonymous)) [8,8 784x0]
        InlinePaintable (InlineNode<DETAILS>)
      PaintableWithLines (ListItemBox<SUMMARY>) [32,8 760x17]
        TextPaintable (TextNode<#text>)
        MarkerPaintable (ListItemMarkerBox(anonymous)) [8,8 12x17]
      PaintableWithLines (BlockContainer<SLOT>) [8,25 784x17]
        InlinePaintable (InlineNode<SPAN>)
          TextPaintable (TextNode<#text>)
      PaintableWithLines (BlockContainer(anonymous)) [8,42 784x0]
