What are the classification rules here?

UNCLASSIFIED ONLY. Everywhere — forum posts, comments, chat, anything you upload. No classified information, no CUI, no program-sensitive details, no aggregating details that shouldn't sit together in public. General questions about what a regulation says are welcome; if answering would require program context, take it to official channels. Moderation enforces this. If you see something that crosses the line, use the report flag — it goes straight to the founder review queue.