bbcode rendering is completely jaxed. There are several hardcoded bbcode values in bbcode.php as well as the useless bbcode_bitfield nonsense that makes bbcode.html useless by default.
There needs to be one transparent method for altering the rendered code template for bbcodes. Which should be bbcode.html.
This allows admin & theme authors to have simulated control over the rendering of the html by the bbcode parser.