[csswg-drafts] [css-nesting] no explicit conjoined examples (#3748)

Dan503 has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-nesting] no explicit conjoined examples ==
CSS nesting spec
https://drafts.csswg.org/css-nesting-1/

There is a very common method of writing BEM classes among FE developers that looks like this when writing in SCSS:

```scss
.block {
  &__element {
    // .block__element { ... }
  }
}
```

The spec currently doesn't seem to explicitly allow for this style of nesting. Providing an example to mention this method is ok is all that would be needed.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/3748 using your GitHub account