The text below says:
Allowed markup: a blockquote br code em strong ul ol li.
It means that these are the tags that can be used. Instead of <b> use the strong tag. Instead of i tage use the em tag. underline isn't supported yet but I'll look into it.
One of the REALLY cool things in the new framework is that even public messages can have markup in it. It has a method to making the text "safe" from javascript attacks. You can use the bold, underline, italics etc. tags in messages. It may not show up properly in the world window but the Previous section it will have it