dfn

used at first mention when a term is defined, and renders enclosed text as italics. It can also be used with CSS or with the ID attribute to simply style and references to definitions within an eBook.
Note: Ignored in version 1.0 of the Microsoft Pocket PC Reader.

attributes

id
Provides an element with a unique name within a single document. This is especially useful in works with extensive cross-referencing and linking, such as dictionaries, encyclopedias, or travel guides. Use of ids simplifies linking and updates.
class
Affiliates an element with one or more classes.
style
Attaches a list of inline (name:value paired) CSS properties to a specific tag, for example: style="name:value;name:value"
Note: Media types other than "text/x-oeb1-css" will be ignored with a warning in a document of type "text/x-oeb1-document".
title
This attribute is ignored.