▽
└─◨ Attr presence: foo
  ┖─◉ Push element: +
    └─◨ Attr presence: bar
      ┠─◁ #1 [0,2,0] value 2
      ┖─◌ Pop element
        └─◨ Attr presence: baz
          ┖─◁ #0 [0,3,0] value 1