In the spec the use of the rp-tag is shown like this:
<ruby> 漢 <rp>(</rp><rt>かん</rt><rp>)</rp> 字 <rp>(</rp><rt>じ</rt><rp>)</rp> </ruby>What semantic function has the rp-tag? No. It is only styling for browsers not supporting ruby-text. So I think this element musn't be in the HTML5 spec. You can add the brackets before and after the ruby text using CSS pseudoclasses (:after, :before).
