src/vs/base/browser/ui/splitview/paneview.ts/PaneView/addPane
class PaneView:	addPane(pane: Pane, size: number, index = this.splitview.length): void {
		const disposables = new DisposableStore();
		pane.onDidChangeExpansionState(this.setupAnimation, this, disposables);

		const paneItem = { pane: pane, disposable: disposables };
		this.paneItems.splice(index, 0, paneItem);
		pane.orientation = this.orientation;
		pane.orthogonalSize = this.orthogonalSize;
		this.splitview.addView(pane, size, index);

		if (this.dnd) {
			const draggable = new PaneDraggable(pane, this.dnd, this.dndContext);
			disposables.add(draggable);
			disposables.add(draggable.onDidDrop(this._onDidDrop.fire, this._onDidDrop));
		}
	}