re: Why I can't find or use <spoil> in group discussion
Custom BBcodes, including [spoiler], were disabled in groups for stability reasons. However, after some reviewing, we've decided that it's probably safe to enable them. Therefore, you can now use [spoiler] and other custom BBcodes in group discussions.
Please consider this decision experimental. If we spot any bugs or stability problems, we'll have to revisit our decision and may again disable custom BBcodes in groups.