When offering a bounty, it is possible to add a custom message. Does this message has to be plain text? Or can we use similar formatting as in the posts? (I.e., MathJax for mathematics, Markdown for formatting. Or perhaps at least the limited version of MarkDown, which is used in comments.)
I am aware that if it is possible, I could simply go through questions which are currently featured or which were featured in the past. Perhaps if I am patient enough, I will find a question where bounty description has MathJax/Markdown.
Another possibility would be to find some bounty-worthy question and then try whether MathJax/Markdown in the bounty description will be displayed.
Despite the fact that this could be verified experimentally without much effort, I think it is good to have documented here on meta whether this is possible or not. (I guess this may be useful for other users who have the same question.)