src/vs/base/browser/ui/splitview/paneview.ts/Pane/setExpanded
class Pane:	setExpanded(expanded: boolean): boolean {
		if (this._expanded === !!expanded) {
			return false;
		}

		this.element?.classList.toggle('expanded', expanded);

		this._expanded = !!expanded;
		this.updateHeader();

		if (expanded) {
			if (!this._bodyRendered) {
				this.renderBody(this.body);
				this._bodyRendered = true;
			}

			if (typeof this.animationTimer === 'number') {
				clearTimeout(this.animationTimer);
			}
			append(this.element, this.body);
		} else {
			this.animationTimer = window.setTimeout(() => {
				this.body.remove();
			}, 200);
		}

		this._onDidChangeExpansionState.fire(expanded);
		this._onDidChange.fire(expanded ? this.expandedSize : undefined);
		return true;
	}