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 readers 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 epub:type
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.
ruby element<p>… so that one can only reasonably conclude that <ruby>the sun revolves around the earth<rt>Contradicts earlier statement.</rt></ruby>. It should be noted that …</p>