I would like to put arbitrary HTML in posts… I know this is probably a bit crazy. But I want to do it. How should I be thinking about this requirement?
To include arbitrary HTML it needs to be whitelisted, trouble is that you do not want a global whitelist of everything cause you open yourself quite wide to arbitrary XSS attacks.
Can you work backwards, what are some examples of problems you are trying to solve?
Having the ability to post arbitrary HTML is equivalent to full admin rights… so no, neither TL4 users nor mods should have that ability, only full admins.