static initClass() {
    this.prototype.type = "Button"
    this.prototype.default_view = ButtonView

    this.define({
      clicks: [ p.Number, 0 ],
    })

    register_with_event(ButtonClick, this)
  }

  static initClass(): void {
    this.prototype.type = "Plot"
    this.prototype.default_view = PlotView

    this.mixins(["line:outline_", "fill:background_", "fill:border_"])

    this.define({
      toolbar:           [ p.Instance, () => new Toolbar()     ],
      toolbar_location:  [ p.Location, 'right'                 ],
      toolbar_sticky:    [ p.Boolean,  true                    ],

      plot_width:        [ p.Number,   600                     ],
      plot_height:       [ p.Number,   600                     ],

      title:             [ p.Any, () => new Title({text: ""})  ], // TODO: p.Either(p.Instance(Title), p.String)
      title_location:    [ p.Location, 'above'                 ],

      h_symmetry:        [ p.Bool,     true                    ],
      v_symmetry:        [ p.Bool,     false                   ],

      above:             [ p.Array,    []                      ],
      below:             [ p.Array,    []                      ],
      left:              [ p.Array,    []                      ],
      right:             [ p.Array,    []                      ],

      renderers:         [ p.Array,    []                      ],

      x_range:           [ p.Instance                          ],
      extra_x_ranges:    [ p.Any,      {}                      ], // TODO (bev)
      y_range:           [ p.Instance                          ],
      extra_y_ranges:    [ p.Any,      {}                      ], // TODO (bev)

      x_scale:           [ p.Instance, () => new LinearScale() ],
      y_scale:           [ p.Instance, () => new LinearScale() ],

      lod_factor:        [ p.Number,   10                      ],
      lod_interval:      [ p.Number,   300                     ],
      lod_threshold:     [ p.Number,   2000                    ],
      lod_timeout:       [ p.Number,   500                     ],

      hidpi:             [ p.Bool,     true                    ],
      output_backend:    [ p.OutputBackend, "canvas"           ],

      min_border:        [ p.Number,   5                       ],
      min_border_top:    [ p.Number,   null                    ],
      min_border_left:   [ p.Number,   null                    ],
      min_border_bottom: [ p.Number,   null                    ],
      min_border_right:  [ p.Number,   null                    ],

      inner_width:       [ p.Number                            ],
      inner_height:      [ p.Number                            ],
      layout_width:      [ p.Number                            ],
      layout_height:     [ p.Number                            ],

      match_aspect:      [ p.Bool,     false                   ],
      aspect_scale:      [ p.Number,   1                       ],
    })

    this.override({
      outline_line_color: "#e5e5e5",
      border_fill_color: "#ffffff",
      background_fill_color: "#ffffff",
    })

    register_with_event(UIEvent, this)
  }