In the next phase caverns or more like passages connecting them went through everything else as was expected. Passages wider than 1 tile were removed temporarily, since there is no routine to check rooms with the ellipse routine drawing passages. It's a minor problem to be fixed later.
Caverns itself were too small for some reason. Fixed that with proper data for the level theme. That way I can control the size on each level theme if needed.
Both actual rooms and caverns are separate "layers" so it's possible that sometimes those two don't have a connection between them. It's rare, but possible. I'm going to check that with flood fill and then searching a place where a corridor can be made without breaking anything else.
When looking at cavern interior generation I started to think too much again. There are 11 different interiors now and some of them are unfinished, but I realized that I can and should leave some of them to do later, namely those I don't need right now in this level theme. It may be even possible that caverns can't do something I need later and I have to create another more specific routine for that task.
Next I'm going to add small rooms which is the last feature for this level theme. After that I'm going to move on next level theme. The idea of the new plan is first create the physical structure of each level theme and only then add details.