BITS 0.2
( app | app-group | floats-group | index | index-group | ref-list | book-part | ack
| bio | dedication | fn-group | glossary | toc | toc-group | notes )+
BITS 1.0
( app | app-group | floats-group | index | index-group | ref-list | book-part | xi:include
| ack | bio | dedication | fn-group | glossary | toc | toc-group | notes )+
BITS 2.0
( book-app | book-app-group | floats-group | index | index-group | ref-list | book-part
| xi:include | ack | bio | dedication | fn-group | glossary | toc | toc-group | notes
)+
BITS 2.1
NO CHANGE IN CONTENT MODEL