require(tag >= 0)
  }

  override fun matches(header: DerHeader): Boolean = header.tagClass == tagClass && header.tag == tag

  override fun fromDer(reader: DerReader): T {
    val peekedHeader = reader.peekHeader()
    if (peekedHeader == null || peekedHeader.tagClass != tagClass || peekedHeader.tag != tag) {
      if (isOptional) return defaultValue as T
      throw ProtocolException("expected $this but was $peekedHeader at $reader")