A layer attribute for layering of linked CSS style sheets in HTML

[mirisuzanne]

こんにちは TAG-さん!

I'm requesting a TAG review of an HTML layer attribute for the <link> tag.

One of the primary use-cases for CSS Cascade Layering is to manage the priority of third-party CSS (libraries and design systems) in relation to site-specific styles. It's currently possible to manage this layering on the CSS @import rule, as defined in CSS Cascading and Inheritance Level 5. However, there are many situations where authors do not want to use @import for performance reasons, or cannot use @import because of build tooling. Providing this functionality on the HTML <link> tag would bring it in better alignment with the CSS import functionality.

There seems to be broad consensus on this aspect of the feature, and I wanted to get formal review in order to hopefully move the conversation forward.

• Explainer¹ (minimally containing user needs and example code): https://css.oddbird.net/layers/link-layer/
• Primary contacts (and their relationship to the specification):
  • Miriam Suzanne (@mirisuzanne), Invited Expert (explainer author & Cascade L5 co-editor)
  • Simon Pieters (@zcorpan), Mozilla (WHATWG contact)
  • Alan Stearns (@astearns), Adobe (CSSWG Co-Chair)
• Organization/project driving the design: CSSWG/WHATWG
• External status/issue trackers for this feature (publicly visible, e.g. Chrome Status): None yet

Further details:

• [x] I have reviewed the TAG's Web Platform Design Principles
• The group where the incubation/design work on this is being done (or is intended to be done in the future): CSSWG & WHATWG
• The group where standardization of this work is intended to be done ("unknown" if not known): WHATWG
• Existing major pieces of multi-implementer review or discussion of this design:
  • (WHATWG #7540) Allow authors to apply new css features (like cascade layers) while linking stylesheets
  • (CSSWG #5853) Provide an attribute for assigning a <link> to a cascade layer
• Major unresolved issues with or opposition to this design: The discussions have generally stalled in trying to provide an additional 'support' condition to stylesheet links, which I will split into a separate explainer.
• This work is being funded by: Some of my work on the feature has been funded by Google Chrome

[jyasskin]

We discussed this in a breakout session with the conclusion that we like it, and we're happy for the WHATWG to figure out the exact name and details. Thanks for working on it!