code: public function get_path($file = '') {
          if (!defined('WP_PLUGIN_DIR')) {
              wp_plugin_directory_constants();
          }
  
          // TODO There is probably better constant than WP_CONTENT_DIR!
          $path = WP_PLUGIN_DIR . DIRECTORY_SEPARATOR . $this->id;
          if (!empty($file)) {
              $path .= DIRECTORY_SEPARATOR . $file;
          }
  
          return $path;
      }
docs: Returns path to the plugin's directory. If `$file` is provided
  than is appended to the end of the path.
  
  @since 0.1.3
  @param string $file (Optional).
  @return string