Here is the list of currently allowed HTML tags and attributes for use in the chatterbox.

Tag Attributes
a href, name, target, title
abbr title
b n/a
blink n/a
c1 n/a
code1 n/a
em n/a
font color
i n/a
small n/a
strong n/a
sub n/a
sup n/a
tt class
u n/a

1Note that <code> and <c> are not really HTML tags at PerlMonks. They prevent enclosed special characters like <, >, &, [, and ] from being interpreted. Also, not even whitespace is allowed inside (< code > will not be recognized) and each must have a matching </code> or </c> for it to work.