The following detail the changes made to the DTD in the 2000-11-01 version. See also the change log.
A new parameter entity was created to make the content models of alternativemath and formula more consistent. Both of these elements now have the same content model: "(math | simplemath | file | tex | alternativemath)+".
Comments listing e.g. acceptable type values deleted from the DTD files. Acceptable values are contained in this documentation. Lists of recommended values may be re-introduced into the *.dtd and *.mod files for use with a validation tool in future.
In documentinfo, more than one date element can now be specified.
A new element, alternativeformat which has a type attribute has been added to the %formatting; parameter entity. This will allow e.g. alternative versions of text strings such as dates, or ascii versions of authors names which might contain diacritics to be specified.
In bookdetails, readergroup replaces readership.
objectgroup has been added to the content model of the %bodytext; parameter entity.
section and subsection have each been given a language attribute. This will allow for accurate identification e.g. of multiple-language tables of contents.