 		private static let compressionMask: UInt8 = 0x07
 		private static let signature: [UInt8] = Array("UTS#46".utf8)
 
-		struct Flags: RawRepresentable {
+		private struct Flags: RawRepresentable {
 			var rawValue: UInt8 {
 				return (hasCRC ? hasCRCMask : 0) | UInt8(compression != nil ? compression!.rawValue + 1 : 0)
 			}

		}

		let version: UInt8
		var flags: Flags
		var hasCRC: Bool { flags.hasCRC }
		var compression: CompressionAlgorithm? { flags.compression }
		var dataOffset: Int { 8 + (flags.hasCRC ? 4 : 0) }


		guard header.version == 1 else { throw UTS46Error.unknownDataVersion }

		let offset = header.dataOffset

		guard fileData.count > offset else { throw UTS46Error.badSize }

