boolean performGuardedChange(Runnable change) {
    if (!myLookupStartMarker.isValid()) {
      throw new AssertionError("Invalid start: " + myEditor + ", trace=" + (myStartMarkerDisposeInfo == null ? null : myStartMarkerDisposeInfo
        .get()));
    }
    change.run();
    return myLookupStartMarker.isValid();
  }
boolean performGuardedChange(Runnable change)