/** Returns true if this adapter can read [header] in a choice. */
  fun matches(header: DerHeader): Boolean

  /**
   * Returns a value from this adapter.
   *
   * This must always return a value, though it doesn't necessarily need to consume data from
   * [reader]. For example, if the reader's peeked tag isn't readable by this adapter, it may return
   * a default value.
   *