START v2 (Softconf): what markup is allowed in reviews?
I emailed Softconf's support and Rich Gerber replied with the following:

The review is always considered a plain text entity, but to display it we insert a bit of markup where we believe markup is warranted.   But *this* will add emphasis, and you can also use bold tags &lt;b&gt;like this&lt;/b&gt;.   There is also implied ordered lists, by numbers starting lines.  You can also insert HTML super and subscripts.  That's about it.

That is:

*emphasis*
&lt;b&gt;bold&lt;/b&gt;
* bulleted list item
1. numbered list item
x&lt;sup&gt;superscript&lt;/sup&gt;
x&lt;sub&gt;subscript&lt;/sub&gt;