This was raised on #4969, related to the Cascade level 5 spec.

We've defined a syntax for cascade layers to be declared as code-blocks or url imports:

@layer reset url(remedy.css); 
@layer reset {
  audio[controls] { display: block; }
}

If we're allowing authors to import entire stylesheets into a layer, it seems appropriate to make that available on <link> and <style> tags as well. For performance reasons, those are more likely to be used - rather than chaining imports. I'm proposing a layer attribute:

<link rel="stylesheet" href="remedy.css" layer="reset">
<style layer="reset">
  audio[controls] { display: block; }
</style>