*
 * For lines that contain a mapping target, the next thing is a sequence of hex code points (like
 * 0031 2044 0034).
 *
 * All other data is ignored.
 */
fun BufferedSource.readPlainTextIdnaMappingTable(): SimpleIdnaMappingTable {
  val mappedTo = Buffer()
  val result = mutableListOf<Mapping>()

  while (!exhausted()) {
    // Skip comment and empty lines.
    when (select(optionsDelimiter)) {