*  * BER: Basic Encoding Rules.
 *
 * This class was implemented according to the [X.690 spec][[x690]], and under the advice of
 * [Lets Encrypt's ASN.1 and DER][asn1_and_der] guide.
 *
 * [x690]: https://www.itu.int/rec/T-REC-X.690
 * [asn1_and_der]: https://letsencrypt.org/docs/a-warm-welcome-to-asn1-and-der/
 */
internal class DerReader(source: Source) {
  private val countingSource: CountingSource = CountingSource(source)