code: func Filter(err error, exclude error, others ...error) error {
  	return FilterFunc(err, func(e error) bool {
  		if e == exclude {
  			return true
  		}
  		for _, v := range others {
  			if e == v {
  				return true
  			}
  		}
  		return false
  	})
  }
docs: // Filter examines a supplied error and removes instances of excluded errors
  // from it. If the entire supplied error is excluded, Filter will return nil.
  //
  // If a MultiError is supplied to Filter, it will be recursively traversed, and
  // its child errors will be turned into nil if they match the supplied filter.
  // If a MultiError has all of its children converted to nil as a result of the
  // filter, it will itself be reduced to nil.