There are times when adding Ruby annotations within the document are necessary. The Ruby Annotations are those which are used for East Asian typography to express the way East Asian characters are pronounced.
The use of HTML5 <rp> tag becomes important if the browser has no support for East Asian typography. The HTML5 <rp> tag is used along with the <ruby> and <rt> tags.
The HTML <rp> tag is just introduced in HTML5. This is non-existent in HTML4.01. However, the good thing is that the HTML5 <rp> tag is compatible with all primary web browsers like Google Chrome, Internet Explorer, Safari, Opera and Firefox. The HTML5 <rp> tag is also supportive of the Global Attributes and Event Attributes in HTML5.