anchor.diff:            savedCursorY = cursorY;
           } else if (_csiC1 == 63) {  // C1 = '?'.
             // TODO(vtl): FIXME soon.
  -assert(false);
  +          assert(!assertFailOnUnimplemented);
           }
           break;
         case 116:  // 't'.
  
positive.code:             case 12:
              case 20:
                // TODO(vtl): FIXME soon.
  assert(false);
                break;
  default:
  // TODO(vtl): FIXME soon.
  assert(false);
  break;
            }
          } else if (_csiC1 == 63) {  // C1 = '?'.
            switch (_csiParams[0]) {
  
negative.code:             case 1061:
              case 2004:
                // TODO(vtl): FIXME soon.
                assert(!assertFailOnUnimplemented);
              default:
                assert(!assertFailOnUnknown);
                break;
            }
          }
          break;
        case 105:  // 'i': Media copy.
          // TODO(vtl): FIXME soon.
          assert(!assertFailOnUnimplemented);
          break;
        case 106:  // 'j': Not actually valid/specified.
          break;
  