7.4. Element body
Specifies the content of a book division (part, chapter, section, etc).
When the
  parent of body is element book then
  body specifies the content of the “title page” of the
  book.
It's possible for a book division to have both an
  href attribute and a body child element. In such
  case, the content “pulled” using the href attribute is inserted
  before the content specified by the body child
  element.
Content model
content+
Attributes
| Name | Data type | Default value | 
|---|---|---|
| xml:base | anyURI | |
| xml:id | ID | |
| xml:lang | languageor "" (the empty string) | . | 
Other attributes: XHTML5 global attributes, including any attribute having
  a name starting with "data-".
Parents
The
  following elements contain body: appendices, appendix, book, chapter, part, section.
Children
The
  following elements occur in body: content.
Example
| 1 2 3 4 5 6 7 8 9 | <chapter> <head> <title>Using Widget</title> </head> <body> <content href="using1.html"/> <content href="using2.html"/> </body> </chapter> |