Custom Functions (@function)

[andruud]

こんにちは TAG-さん!

I'm requesting a TAG review of Custom Functions (@function)

"A custom function can be thought of as an advanced custom property, which instead of being substituted by a single fixed value provides its substitution value based on function parameters and local variables." (From the spec.)

• Explainer¹: https://css.oddbird.net/sasslike/mixins-functions/ (Also explains mixins, which is not in scope for this review.)
• Specification: https://drafts.csswg.org/css-mixins-1/#defining-custom-functions
• WPT Tests: N/A
• User research: https://css.oddbird.net/sasslike/mixins-functions/#author-interest
• Security and Privacy self-review²:
  tl;dr: nothing to report, expand for details.

  • 2.1 What information might this feature expose to Web sites or other parties, and for what purposes is that exposure necessary?
    A: It doesn't expose anything. It's both defined and used within CSS.
  • 2.2 Do features in your specification expose the minimum amount of information necessary to enable their intended uses?
    A: Yes. (Nothing.)
  • 2.3 How do the features in your specification deal with personal information, personally-identifiable information (PII), or information derived from them?
    A: N/A
  • 2.4 How do the features in your specification deal with sensitive information?
    A: N/A
  • 2.5 Do the features in your specification introduce new state for an origin that persists across browsing sessions?
    A: No.
  • 2.6 Do the features in your specification expose information about the underlying platform to origins?
    A: No.
  • 2.7 Does this specification allow an origin to send data to the underlying platform?
    A: No.
  • 2.8 Do features in this specification enable access to device sensors?
    A: No.
  • 2.9 Do features in this specification enable new script execution/loading mechanisms?
    A: No.
  • 2.10 Do features in this specification allow an origin to access other devices?
    A: No.
  • 2.11 Do features in this specification allow an origin some measure of control over a user agent's native UI?
    A: No.
  • 2.12 What temporary identifiers do the features in this specification create or expose to the web?
    A: None.
  • 2.13 How does this specification distinguish between behavior in first-party and third-party contexts?
    A: N/A.
  • 2.14 How do the features in this specification work in the context of a browser's Private Browsing or Incognito mode?
    A: As normal / not applicable.
  • 2.15 Does this specification have both "Security Considerations" and "Privacy Considerations" sections?
    A: Not yet.
  • 2.16 Do features in your specification enable origins to downgrade default security protections?
    A: N/A.
  • 2.17 How does your feature handle non-"fully active" documents?
    A: N/A.
  • 2.18 What should this questionnaire have asked?
    A: N/A.
• GitHub repo: https://github.com/w3c/csswg-drafts/tree/main/css-mixins-1
• Primary contacts:
  • @mirisuzanne, CSSWG Invited Expert, original proposal author and spec editor.
  • @tabatkins, Google, spec editor.
  • @andruud, Google, working on the feature in Chromium.
• Organization/project driving the specification: Chromium
• Multi-stakeholder support³:
  • Chromium comments: 👍
  • Mozilla comments: CSS Functions and Mixins 1 (@function) mozilla/standards-positions#1148
  • WebKit comments: CSS Functions and Mixins 1 (@function) WebKit/standards-positions#437
• Status/issue trackers for implementations⁴: https://issues.chromium.org/issues/325504770

Further details:

• I have reviewed the TAG's Web Platform Design Principles
• Relevant time constraints or deadlines: Q1 2025.
• The group where the work on this specification is currently being done: CSSWG
• The group where standardization of this work is intended to be done (if different from the current group): CSSWG
• Major unresolved issues with or opposition to this specification: [css-mixins] Improve ergonomics of using by allowing wildcards w3c/csswg-drafts#10954 (not opposition, but could lead to removal of the using keyword and associated behavior.)
• This work is being funded by: N/A

[LeaVerou]

There has been some CSS WG discussion around dropping using and just using the local context where the function is used, yet this explainer still includes it. Is it not removed or is the explainer outdated?

[mirisuzanne]

It's likely the explainer is out of date - although I'm not sure there were any resolutions or decisions, only some conversation in the github threads.

[andruud]

I think it's reasonable to keep using in the explainer until w3c/csswg-drafts#10954 is resolved.

The discussion in that issue does seem to converge on using being dropped, though.

[LeaVerou]

I think it's reasonable to keep using in the explainer until w3c/csswg-drafts#10954 is resolved.

The discussion in that issue does seem to converge on using being dropped, though.

It seems like it's going to resolve imminently, so could you ping us when it resolves so we could review then?

[andruud]

Yes, will do.