Yeah, there are 3 types of code I can use:
HTML macros, which look like <br> and <div>
Twine macros, which look like <<if>> and <<nobr>>
And javascript commands, which look like Math.round().
Of the first two types, some macros are alone, like <br>, and some require closing statements, like </div> and <</nobr>>. Specifically, there has to be exactly 1 closing statement for every opening statement, otherwise it'll show an error. It may still work as advertised, but that big red box is pretty distracting.
I know I put a <<nobr>> there after seeing the error the first time, but I bet I put it slightly out of place, like [( ]). Totally wonky