The correct use of annotations enhances the reading experience in the same way that the correct application of notes does: it unclutters the primary narrative and allows users to selectively choose what they want to read.
The Open Annotation in EPUB specification defines a serialization format for including annotations in an EPUB Publication.
Inline annotations can also be included using the HTML5
ruby element. Although commonly used
for annotating east Asian languages, there is no restriction on their use. An
attribute is not required when using the
ruby element, since it is defined for such use.
Note that when using the
ruby element for lengthy annotations, unwanted whitespace can be
introduced before and after the annotated text to accommodate the overline (or underline) run.