~~**CommaListExpression** ::= SpaceListExpression (',' SpaceListExpression)*~~
**CommaListExpression** ::= SlashListExpression (',' SlashListExpression)*
**SlashListExpression** ::= SpaceListExpression ('/' SpaceListExpression)*
> Note that `/` may *not* be used in single-element lists the way `,` is. That
> is, `(foo,)` is valid, but `(foo/)` is not.
>
> This defines `/` to bind tighter than `,` but looser than space-separated
> lists. This was chosen because most common uses of `/` in CSS conceptually
> bind looser than space-separated values. The only exception is the [`font`
> shorthand syntax][], which is used much more rarely will still work (albeit
> with an unintuitive SassScript representation) with a loose-binding `/`.
>
> [`font` shorthand syntax]: https://developer.mozilla.org/en-US/docs/Web/CSS/font
It also modifies the existing `ProductExpression` production to remove `/` as an
operator. The new grammar for this production is: