<?php

namespace Customizer;

abstract class Core {

	public function add_section( Section $section ) {

	}

	public function remove_section( Section $section ) {

	}

}

<?php

namespace Customizer;

abstract class Core {

	private $sections;

	public function add_section( Section $section ) {

	}

	public function remove_section( Section $section ) {

	}

}

Add sections instance variable to customizer core
Add sections instance variable to customizer core
