src/vs/base/browser/ui/sash/sash.ts/Sash/orthogonalStartSash
class Sash:	set orthogonalStartSash(sash: Sash | undefined) {
		this.orthogonalStartDragHandleDisposables.clear();
		this.orthogonalStartSashDisposables.clear();

		if (sash) {
			const onChange = (state: SashState) => {
				this.orthogonalStartDragHandleDisposables.clear();

				if (state !== SashState.Disabled) {
					this._orthogonalStartDragHandle = append(this.el, $('.orthogonal-drag-handle.start'));
					this.orthogonalStartDragHandleDisposables.add(toDisposable(() => this._orthogonalStartDragHandle!.remove()));
					this.orthogonalStartDragHandleDisposables.add(new DomEmitter(this._orthogonalStartDragHandle, 'mouseenter')).event
						(() => Sash.onMouseEnter(sash), undefined, this.orthogonalStartDragHandleDisposables);
					this.orthogonalStartDragHandleDisposables.add(new DomEmitter(this._orthogonalStartDragHandle, 'mouseleave')).event
						(() => Sash.onMouseLeave(sash), undefined, this.orthogonalStartDragHandleDisposables);
				}
			};

			this.orthogonalStartSashDisposables.add(sash.onDidEnablementChange.event(onChange, this));
			onChange(sash.state);
		}

		this._orthogonalStartSash = sash;
	}