Nested module: use layout of parent module

I’ve got a nested module, and I’d like to use the layout of the parent module. How can I do that? Neither of the following options work:

	public $layout = '//layouts/column1'; // The application layout is used

	public $layout = '/layouts/column1'; // The current module layout is used

The doc says that you can use the parent module’s layout by setting “layout” to null.

Or, you may want to specify “layoutPath” to point to the parent module’s layout path.