How to use the elm.so.Box function in elm

if (this.didChangeURI)
          this.didChangeURI(uri);
      }.bind(this),

      on_link_hover_in: function(uri, title) {
        this.link_hover_notify.visible = true;
        this.link_hover_notify.content.text = uri;
      }.bind(this),

      on_link_hover_out: function() {
        this.link_hover_notify.visible = false;
      }.bind(this)
    });

    this.viewDescriptor = elm.Box({
      expand: 'both',
      fill: 'both',
      horizontal: false,
      elements: {
        web: web,
        progress: progress, /* FIXME get this out of the box */
        link_hover_notify: link_hover_notify /* FIXME get this out of the box */
      },
    });
  },

_showPopup: function(possible_handlers) {
    this.popup.content.content['eui.swallow.content'] = elm.Box({
      horizontal: false,
      elements: {}
    });

    var buttons = this.popup.content.content['eui.swallow.content'];
    for (var i = 0; i < possible_handlers.length; ++i) {

      buttons.elements[i] = elm.Button({
        label: possible_handlers[i].name,
        fill: 'horizontal',
        index: i,
        on_click: function(item) {
          print("eval(" + possible_handlers[item.index].app + ")");
          this._hidePopup();
        }.bind(this)
      });

_createNavigationBarItems: function(items) {
    if (items === undefined || items.length === 0)
      return;
    if (items.length == 1)
      return this._createNavigationBarItem(items[0]);

    var elements = [];
    for (var i = 0, j = items.length; i < j; ++i)
      elements.push(this._createNavigationBarItem(items[i]));

    return elm.Box({ horizontal: true, elements: elements });
  },