RE: [css-syntax] At-rules mixed in any declaration list?

>>> @page {
>>> @margin-note { /* not supported */ }
>>> background: green;
>>> }
>
> My point is that even we don’t define any such at-rule yet, this does
> make a detectable difference in error handling. It was important that
> CSS 2.1 defined @page that way, for example.

Not necessarily. We could force at-rules to come after all the declarations OR be followed by a semi-colon.