We will make the following backwards-incompatible changes in V3.0:
The SpanEnd attribute on IndexTerm will be renamed StartRef to indicate that it points to the content of the IndexTerm being spanned. A Class attribute will be added to indicate whether the IndexTerm element is the beginning point of a span (StartOfRange), the ending point (EndOfRange), or a standalone index term (Singular).
FootnoteRef will be declared EMPTY and its Mark attribute renamed Label.
RevHistory will require at least one Revision.