anchor.diff:              case 12:
               case 20:
                 // TODO(vtl): FIXME soon.
  -assert(false);
  -              break;
  -default:
  -// TODO(vtl): FIXME soon.
  -assert(false);
  -break;
  +              assert(!assertFailOnUnimplemented);
  +              break;
  +            default:
  +              assert(!assertFailOnUnknown);
  +              break;
             }
           } else if (_csiC1 == 63) {  // C1 = '?'.
             switch (_csiParams[0]) {
  
positive.code:           }
          } else if (_csiC1 == 63) {  // C1 = '?'.
            // TODO(vtl): FIXME soon.
  assert(false);
          }
          break;
        case 115:  // 's'.
  
negative.code:       case 125:  // '}'.
        case 126:  // '~'.
          // TODO(vtl): FIXME soon.
          assert(!assertFailOnUnimplemented);
          break;
        default:
          assert(!assertFailOnUnknown);
          break;
      }
  
      state = TerminalModelState.NORMAL;
  