which messages it will respond to, and what its behaviour will be when it
receives them. The property value must be an identifier naming a defined
subclass of @"SodClass". The default metaclass is @"SodClass".
- %%% FIXME xref to theory
+ See \xref{sec:concepts.metaclasses} for more details.
\item[@"nick"] A nickname for the class, to be used to distinguish it from
other classes in various limited contexts. The property value must be an
identifier; the default is constructed by forcing the class name to