[css-hierarchies] Why require the & character?

Forking to a new thread, trimming the cc list accordingly.

On Mon, Sep 2, 2013 at 8:15 AM, Brad Kemper <brad.kemper@gmail.com> wrote:
> Slightly off topic:
> Hierarchies has not received a lot of review yet, but my view so far is that writing "&" so many times makes it more likely that it will be accidentally left off. I can see why you'd want it when modifying the outer selector with a class, pseudo-class, attribute selector, etc., but why is it needed for embedded rules that could have continued the outer rule with a space character?

Because the grammar is ambiguous without it - you can't tell apart
some types of selectors from properties without arbitrary lookahead.

That said, I'm not actually happy with what Hiearchies currently
specifies, which is part of why I haven't been pushing on it lately.
I think we either need to bite the bullet and do an @nest rule inside
of the style rule which then contains plain selectors (with &
optionally used to indicate the parent selector), or figure out a
"good enough" parsing compromise that lets us tell selectors and
properties apart within a small, bounded number of tokens at the
parser level, at the cost of sometimes misinterpreting
previously-valid CSS.

Example of the problem: If you see "foo:bar baz qux ...", that could
either be a property named "foo" with a value of "bar baz qux ...", or
a selector starting with a type selector of "foo" and a pseudoclass of
":bar", plus more selectors following.  You can't tell either way for
sure until you hit a ";" or "}" character (it was a property) or a "{"
character (it was a selector).

~TJ