On Sat, 13 Jul 2002, Ingo Mittendorf wrote:
> "Class extension is always clean in that the set of documents matching the
> DTD containing the extended class contains all of the documents matching the
> original DTD. Class extension can imply either ***the addition of an
> existing element to a pre-defined class***, or the addition of a new element
> (as described in the next section) to one."
> [Guidelines, 29.1.3., last paragraph]
> That's basically a go-ahead.
I agree that the text may be read to imply that "addition of an existing
element to a predefined class" does not preclude changing existing class
membership. However, I believe that the intention of this clause was to
permit addition of an existing *unclassified* element to an existing