code: public function synchronize()
  	{
  		if (!$this->isUnsynchronized())
  		{
  			return;
  		}
  
  		// Check if the .nosync file exists
  		if (!file_exists($this->strRootDir . '/' . $this->strFolder . '/.nosync'))
  		{
  			throw new \RuntimeException(sprintf('Cannot synchronize the folder "%s" because one of its parent folders is unsynchronized', $this->strFolder));
  		}
  
  		(new File($this->strFolder . '/.nosync'))->delete();
  	}
docs: Synchronize the folder by removing the .nosync file
  
  @throws \RuntimeException If one of the parent folders is unsynchronized