Should the & operator perform a cartesian product?

[Pierre-Yves Gérardy]

With SASS and LESS (but not Stylus),

p, a {
    & + & {
        color: red;
    }
}

Expands to

p + p, a + p, p + a, a + a {
  color: red;
}

It may be nice to emulate that behavior, for consistency.

[Pierre-Yves Gérardy]

Not sure it should, but it now does in the v1_preview branch.