Deleting Filled Regions Types...

Today I was asked to clean up some filled regions types. It took 30 minutes to figure out how to do that.
First of all, I tried the Object Styles panel, but Filled Regions are not showed there. So I went into Settings, but there is nothing about filled Regions there either. Finally, I browse the family tree, and under Detail Items / Filled Regions I found all the types that existed in the project. I select a few that I wanted to get rid of and... No delete possible. Either used, or unused, the Delete command is grayed out, and the Delete key does nothing. Great.
Finally, the only thing that works is Purge Unused. Go in, uncheck all, and re-check the Filled Regions types that you do not want. In this environment, you will see only the Filled Region types NOT USED in the project.

PS: Same thing happens if you would like to delete Dimension Types...