code: public function register()
      {
          if ($this->registered) {
              return;
          }
          $this->prevDisplayErrors = \ini_set('display_errors', 0);
          $this->prevErrorHandler = \set_error_handler(array($this, 'handleError'));
          $this->prevExceptionHandler = \set_exception_handler(array($this, 'handleException'));
          $this->registered = true;   // used by this->onShutdown()
          return;
      }
docs: Register this error handler and shutdown function
  
  @return void