src/vs/workbench/browser/parts/editor/sideBySideEditor.ts/SideBySideEditor/setOptions
class SideBySideEditor:	override setOptions(options: ISideBySideEditorOptions | undefined): void {
		super.setOptions(options);

		// Update focus if target is provided
		if (typeof options?.target === 'number') {
			this.lastFocusedSide = options.target;
		}

		// Apply to focused side
		this.getLastFocusedEditorPane()?.setOptions(options);
	}