 public enum StringsFileParserError: Error, CustomStringConvertible {
   case failureOnLoading(path: String)
   case invalidFormat
+  case invalidPlaceholder(previous: StringsFileParser.PlaceholderType, new: StringsFileParser.PlaceholderType)
 
   public var description: String {
     switch self {

      return "Failed to load a file at \"\(path)\""
    case .invalidFormat:
      return "Invalid strings file"
    }
  }
}

          while list.count <= insertionPos-1 {
            list.append(.unknown)
          }
          let previous = list[insertionPos-1]
          guard previous == .unknown || previous == p else {
            throw StringsFileParserError.invalidPlaceholder(previous: previous, new: p)
          }
          list[insertionPos-1] = p
        }
      }
