Subschematic Structure Limitations

[DoctorJohnSmith]

Please add the ability to add structure limitations such as blacklist spawn blocks to sub schematics. For complex structures, such as a a dungeon that generates randomly this could be used to stop the structure from generating if it will end up generating on top of itself.

For my use case I have standard sized modules, the center part where the schematic is created from and placed at uses a specific block. Signs to generate the next segment are placed in mid air using setblock, where the next segment should generate. If the specific block is already present, placed by a previous structure segment, it would prevent generating more structure over the existing one.