From Web Education Community Group
The <rp> element can be used to provide parentheses around a ruby text component of a ruby annotation.
- Parentheses be shown by user agents that don't support ruby annotations.
See global attributes.
The example above, in which each ideograph in the text 漢字 is annotated with its phonetic reading, could be expanded to use rp so that in legacy user agents the readings are in parentheses [try it]:
<p> ... <ruby> 漢 <rp>(</rp><rt>かん</rt><rp>)</rp> 字 <rp>(</rp><rt>じ</rt><rp>)</rp> </ruby> ... </p>
The HTML5 specification defines the <rp> element in 4.6.21 The rp element.