CSS Print corner case

[cmahnke]

This is probably not a real bug, but a current limitation of the model. The CSS Paged Media Module Level 3 (and earlier versions) describe a @page at-rule:

Example 2 of the specification

@page :left {
margin-left: 3cm;
margin-right: 4cm;
}

@page :right {
margin-left: 4cm;
margin-right: 3cm;
}

Translated to SASS this should look like this:

@page {
  size: 210mm 210mm !important;
  margin-top: 1cm;
  margin-bottom: 1cm;

  & :left {
    margin-left: 1cm;
    margin-right: 2cm;
  }

  & :right {
    margin-left: 2cm;
    margin-right: 1cm;
  }
}

But this currently not supported: Top-level selectors may not contain the parent selector "&". Please consider enhancing the model to support such constructs.
The example might not make it not instantly clear, but taking into account that there is also the concept of a named page (think of templates for types like foreword, TOC, indexes) this will certainly make more sense.
I'm aware the the CSS printing (and related) modules aren't very well supported by browsers, but they are by specialized tools, see print-css.rocks.

[ntkme]

The error is expected, and it isn’t any corner case.

@page is an at-rule instead of a selector. & only expands to the parent selector. In this case there isn’t any parent selector. & won’t combine an at-rule with a selector.

Also, :left, :right, etc. are special page-selectors instead of normal element selectors by the syntax definition: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@page#formal_syntax

[cmahnke]

Well, I'm aware of that, that's the reason why I wrote that this isn't a classical bug.

My question was if it might be possible to have a special case where &doesn't combine with a parent selector but with a parent something (which would be an at-rule in this case).

I haven't looked into it, but maybe this can be beneficial for other at-rules as well...