Version 2.3 was released on March 28, 2007.
The files for Version 2.3 are available:
by anonymous FTP: ftp://ftp.ncbi.nih.gov/pub/archive_dtd/books/historical/
The Tag Library for version 2.3 is here: http://dtd.nlm.nih.gov/book/historical/tag-library/2.3/
A full list of updates in version 2.3 is available in the Change Report.
A Frequently Asked Questions page is available.
Last updated: October 3, 2008