A new preliminary draft of mads is available, at:

The major change in this draft (from the December 17 draft) is the reference
to a type library.  (In addition, the error with the 'group' is fixed.)

We did not make the change to enforce the suggested rule that descriptor
types for variants be the same as those for authorities,  because our
analysis led us to conclude that such a rule was not valid.

We have begun a type library, a schema of data definitions common to MADS
and MODS (and perhaps additional related future schemas).  The working name
for this type library is "mstl" (metadata schema type library).  It's at:

In addition I have put up a version of mods that uses this type library:
This is not intended as a first draft of mods version 4, it's more like an
idea of what a new version of mods might look like if the current draft of
mads were stable, which it is not. When the first official version of mads
is available then we would like to start looking at a new version of mods,
which would reference the type library (reflected in this draft).