Not a bug Spoiler Nesting

If a spoiler with a lot of nesting like this, placing it in a signature or message starts to travel outside the page.
For an example, see thix

It is possible to do this sort of thing with some other tags as well. In general, it's not really something we're aiming to prevent. There are various things that your users could do which is reasonable up to some point but then becomes annoying -- this is something you would likely need to take a view on and handle via manual moderation.