When the document has to have East Asian typography, using the HTML5 <rt> tag is a big help. It is the tool used for providing the explanation or pronunciation of the typography used. The HTML5 <rt> tag is used along with the <ruby> and <rp> tags to clearly define he ruby annotations.
The HTML5 <rt> tag is a new element in HTML5 and this is not used in HTML4.01. Even if it is new, this is recognized in web browsers like Internet Explorer, Firefox, Opera, Google Chrome and Safari. It is also supportive of the Global Attributes and Event Attributes in HTML5.