public static function initialize( array $defaults, Options $options, $options_key ) {

		// Create controls from default configuration.
		$controls = [];
		$groups   = [];
		foreach ( $defaults as $control_id => $control_info ) {
			$controls[ $control_id ] = $control_info['ui']::create( $options, $options_key, $control_id, $control_info );

			if ( ! empty( $control_info['grouped_with'] ) ) {
				$groups[ $control_info['grouped_with'] ][] = $control_id;
			}
		}

		// Group controls.
		foreach ( $groups as $group => $control_ids ) {
			foreach ( $control_ids as $control_id ) {
				$controls[ $group ]->add_grouped_control( $controls[ $control_id ] );
			}
		}

		return $controls;
	}