code: func (f FieldMatchingFlags) IsSet(flag FieldMatchingFlags) bool {
  	if flag == DestFromSource {
  		// The bit logic doesn't work on the default value.
  		return f&SourceToDest != SourceToDest
  	}
  	return f&flag == flag
  }
docs: // IsSet returns true if the given flag or combination of flags is set.