While we are discussing rendering, there is one more bit of markup that we have not yet explored. If a user agent doesn't understand how to display ruby text, it will just display the base text immediately followed by the ruby text, using the same font size (as shown in the slide). This will be confusing to the reader.

The rp (ruby parenthesis) element allows you to specify characters that will appear around simple ruby text if the user agent doesn't support ruby presentation. You are most likely to want to use parentheses here, but any character or sequence of characters is valid.