doc: /* Make SYMBOL a variable alias for symbol ALIASED.
Setting the value of SYMBOL will subsequently set the value of ALIASED,
and getting the value of SYMBOL will return the value ALIASED has.
-Third arg DOCSTRING, if non-nil, is documentation for SYMBOL.
+Third arg DOCSTRING, if non-nil, is documentation for SYMBOL. If it is
+omitted or nil, SYMBOL gets the documentation string of ALIASED, or of the
+variable at the end of the chain of aliases, if ALIASED is itself an alias.
The return value is ALIASED. */)
(symbol, aliased, docstring)
Lisp_Object symbol, aliased, docstring;