GC_Customize_Widgets::filter_dynamic_sidebar_params()

	public function filter_dynamic_sidebar_params( $params ) {
		$sidebar_args = array_merge(
			array(
				'before_widget' => '',
				'after_widget'  => '',
			),
			$params[0]
		);

		// Skip widgets not in a registered sidebar or ones which lack a proper wrapper element to attach the data-* attributes to.
		$matches  = array();
		$is_valid = (
			isset( $sidebar_args['id'] )
			&&
			is_registered_sidebar( $sidebar_args['id'] )
			&&
			( isset( $this->current_dynamic_sidebar_id_stack[0] ) && $this->current_dynamic_sidebar_id_stack[0] === $sidebar_args['id'] )
			&&
			preg_match( '#^<(?P<tag_name>w+)#', $sidebar_args['before_widget'], $matches )
		);
		if ( ! $is_valid ) {
			return $params;
		}
		$this->before_widget_tags_seen[ $matches['tag_name'] ] = true;

		$context = array(
			'sidebar_id' => $sidebar_args['id'],
		);
		if ( isset( $this->context_sidebar_instance_number ) ) {
			$context['sidebar_instance_number'] = $this->context_sidebar_instance_number;
		} elseif ( isset( $sidebar_args['id'] ) && isset( $this->sidebar_instance_count[ $sidebar_args['id'] ] ) ) {
			$context['sidebar_instance_number'] = $this->sidebar_instance_count[ $sidebar_args['id'] ];
		}

		$attributes                    = sprintf( ' data-customize-partial-id="%s"', esc_attr( 'widget[' . $sidebar_args['widget_id'] . ']' ) );
		$attributes                   .= ' data-customize-partial-type="widget"';
		$attributes                   .= sprintf( ' data-customize-partial-placement-context="%s"', esc_attr( gc_json_encode( $context ) ) );
		$attributes                   .= sprintf( ' data-customize-widget-id="%s"', esc_attr( $sidebar_args['widget_id'] ) );
		$sidebar_args['before_widget'] = preg_replace( '#^(<w+)#', '$1 ' . $attributes, $sidebar_args['before_widget'] );

		$params[0] = $sidebar_args;
		return $params;
	}