em
Indicates that the text within the tags should be rendered with some form of emphasis. Authors should attempt to use the em and strong tags in place of the b, i and u tags, except where explicit control over text presentation is required.

attributes

id
Provides an element with a unique name within a single deck.
class
Affiliates an element with one or more classes.
xml:lang
Specifies the natural or formal language in which the document is written.