<script>
// Created by Omikron 9861 of Aetus Designs (aetus.net)
function custombbc(BBC,HTML,CLOSING_BBC,CLOSING_HTML){var b=document.getElementsByTagName("div");for(x=0;x<b.length;x++){if(b[x].className=="post"&&b[x].innerHTML.match(BBC+"(.*)+"+CLOSING_BBC)){b[x].innerHTML=b[x].innerHTML.split(BBC+RegExp.$1+CLOSING_BBC).join(HTML+RegExp.$1+CLOSING_HTML);}}}
custom_bbc('[bbc]','html','[/bbc]','close html');
</script>
To add more BBC, at the end add more lines like the one above. For example, if I wanted a [bold] BBC, I'd put
custom_bbc('[bold]','<b>','[/bold]','</b>');
Just before the </script> line.
This is like v1 except for the fact that, thanks to slayer, there is no more limitation of being able to use only one per post.