/**
   * `source.length` may be longer than the max length of the variant's data frame. Implementations
   * must send multiple frames as necessary.
   *
   * @param source the buffer to draw bytes from. May be null if byteCount is 0.
   * @param byteCount must be between 0 and the minimum of `source.length` and [maxDataLength].
   */
  @Throws(IOException::class)
  fun data(
    outFinished: Boolean,