Source

File: wp-includes/class-wp-customize-widgets.php

public function get_widget_control_parts( $args ) {
		$args[0]['before_widget_content'] = '<div class="widget-content">';
		$args[0]['after_widget_content']  = '</div><!-- .widget-content -->';
		$control_markup                   = $this->get_widget_control( $args );

		$content_start_pos = strpos( $control_markup, $args[0]['before_widget_content'] );
		$content_end_pos   = strrpos( $control_markup, $args[0]['after_widget_content'] );

		$control  = substr( $control_markup, 0, $content_start_pos + strlen( $args[0]['before_widget_content'] ) );
		$control .= substr( $control_markup, $content_end_pos );
		$content  = trim(
			substr(
				$control_markup,
				$content_start_pos + strlen( $args[0]['before_widget_content'] ),
				$content_end_pos - $content_start_pos - strlen( $args[0]['before_widget_content'] )
			)
		);

		return compact( 'control', 'content' );
	}