Jan Vroonhof <vroonhof(a)math.ethz.ch&gt; writes: I know how you feel -- I tried to do that, and I gave up. Note that it would be possible to compatibly add new specifier tags for all domains, e.g. by a new DOMAINS optional argument to `define-specifier-tag', or by a new function `define-specifier-tag-in-domains'. However, the problem is that the current specifier implementation has to be extended to support such on-the-fly fetching of relevant data. I believe Kirill did some work on this, but it was never finished.