docs: def install_handler(self, app):
          """Install log handler on Flask application."""
          # Check if directory exists.
          basedir = dirname(app.config['LOGGING_FS_LOGFILE'])
          if not exists(basedir):
              raise ValueError(
                  'Log directory {0} does not exists.'.format(basedir))
  
          handler = RotatingFileHandler(
              app.config['LOGGING_FS_LOGFILE'],
              backupCount=app.config['LOGGING_FS_BACKUPCOUNT'],
              maxBytes=app.config['LOGGING_FS_MAXBYTES'],
              delay=True,
          )
          handler.setFormatter(logging.Formatter(
              '%(asctime)s %(levelname)s: %(message)s '
              '[in %(pathname)s:%(lineno)d]'
          ))
          handler.setLevel(app.config['LOGGING_FS_LEVEL'])
  
          # Add handler to application logger
          app.logger.addHandler(handler)
  
          if app.config['LOGGING_FS_PYWARNINGS']:
              self.capture_pywarnings(handler)
  
          # Add request_id to log record
          app.logger.addFilter(add_request_id_filter)