[@Kuro]

On one hand, it won't mess up any RPs that rely on broken BBCode functions right now—it's not retroactive.

As for BBCode-heavy RPs, it shouldn't mess anything up unless they decide to make a post with errors in it (and if they do, even the existing Guild system will break those posts—it just doesn't try to self-correct and recover). I really like the spellcheck suggestion and I can easily add something like "misaligned tag <tagName> at character <number>." I can try to add something that highlights the error too.