While chatting about data recovery, an obscure filesystem has come up. It has a MBR partition ID (maybe?) — but while it appears in those ID tables there is never any indication of where it came from or where it is used. Some of them even suggest that this partition ID is only rumoured to exist.
Would asking about this filesystem's existence/use be within the scope of this site?
I do not have an actual example or evidence of its existence; it seems in the modern world this name only ever comes up when partition tables are corrupted.