code: func IsErrFilePos(err error) bool {
  	if err == nil {
  		return false
  	}
  	_, isErrFilePos := err.(ErrFilePos)
  	return isErrFilePos
  }
docs: // IsErrFilePos identifies whethere or not the root cause of the provided error is of the ErrFilePos type.
  // Wrapped errors are unwrapped via the Cause() function.