It isn’t really that important, and more of a question thread as to why (probably filters mistaking it for something else)
My friend was having trouble posting something in a group, and after a few moments of testing various phrases it turns out if you enter it on a group wall it returns an error and doesn’t post it.
Edit: just tried typing it in here and it made everything after it invisible
Fun fact: I used sdfsdfsd</html> as a password on an alternate count once just to see what would happen and I would get an error page every time I tried to log in :P