Declares that \var{function} should be used as a ``reduction''
function for objects of type \var{type}; \var{type} should not a
class object. \var{function} should return either a string or a
- tuple. The optional \var{constructor} parameter, if provided, is a
+ tuple containing two or three elements.
+
+ The optional \var{constructor} parameter, if provided, is a
callable object which can be used to reconstruct the object when
called with the tuple of arguments returned by \var{function} at
pickling time. \exception{TypeError} will be raised if
\var{object} is a class or \var{constructor} is not callable.
+
+ See the \refmodule{pickle} module for more
+ details on the interface expected of \var{function} and
+ \var{constructor}.
\end{funcdesc}