Here's the first version of my XBBCode module.
Please note three things:
1. I have never developed a software product ready for deployment.
2. This is not yet intended for production.
3. My blog loads very slowly these days. Guess why.
I have left the "no cache" flag on in the filter to make debugging easier; meanwhile, the filter is kind of inefficient.
Honestly, this is less interesting to you as a tool than as a proof of concept work that will be interesting to look at and improve. However, it is functional.
And now, here we go.