The file examples/should_fail/unclassified_at_level_0.xml is deemed invalid here, but is accepted by XModeler. There, it looks as follows:

The reason it is considered invalid here is that it seems useless to have something at level 0 that is not concretizing something from higher levels.
The file examples/should_fail/unclassified_at_level_0.xml is deemed invalid here, but is accepted by XModeler. There, it looks as follows:

The reason it is considered invalid here is that it seems useless to have something at level 0 that is not concretizing something from higher levels.