Standard for union initialization?

[Doug Gwyn <gwyn>]

> union {
>     <type1> foo;
>     <type2> bar;
>     <type3> mumble;
> } baz = (type3) <initializer>;

This is the closest thing to a solution yet.
Still hard to fit into a regular grammar,
since "(type)constant" is already understood
as a valid constant in this context.
However, if the "initialize first member"
rule is adopted, the above example would still
work in some (not all) cases.