Early customizable select feature

[captainbrosset]

Customizable select has been in discussions and in various states of prototypes for a few years already. It's feeling like the proposal is stabilizing now, and the feature has reached WHATWG stage 2 (soon stage 3). See this developer.chrome.com blog about it.

We've talked about how some (most?) features might need to get created early in the making, and I wanted to see what it felt like for this one.

@SachaG had asked for it in the past, in order to be able to link to it from State of HTML, where it's mentioned.

[captainbrosset]

One obvious problem with creating this early feature is the lack of official spec. I think the most official artefact we have for this feature is the explainer on openui.org, which is what I've used for now, but which breaks the build.

[josepharhar]

This link should be updated to https://open-ui.org/components/customizableselect/

[captainbrosset]

Isn't this the same link that's already there in the file?

[captainbrosset]

Chromium I2S is out: https://groups.google.com/a/chromium.org/g/blink-dev/c/kN5LTzuTLVs/m/6HqTsmk3EQAJ

[captainbrosset]

One obvious problem with creating this early feature is the lack of official spec. I think the most official artefact we have for this feature is the explainer on openui.org, which is what I've used for now, but which breaks the build.

Based on the html spec PR, there are actually multiple spec additions that cover what's needed for customizable select:

Spec PRs:

• Relax <select> parser whatwg/html#10557
• Update content model for customizable select whatwg/html#10586
• Define base appearance for <select> whatwg/html#10629
• Define the <selectedcontent> element whatwg/html#10633
• Add UA stylesheet for <select> base appearance whatwg/html#10670

CSS spec PRs:

• [css-ui-4] Define appearance:base w3c/csswg-drafts#10691
• [css-pseudo-4] Define ::picker() w3c/csswg-drafts#10865
• [css-pseudo-4] Fix grammar for ::picker w3c/csswg-drafts#10936
• [css-forms-1] Add new pseudo-elements for customizable select w3c/csswg-drafts#10986

Accessibility PRs:

• Update: add mapping tables for customizable select w3c/aria#2369
• [html-aam] Addition: selectedcontent element w3c/aria#2344
• Add <selectedcontent> element w3c/html-aria#528
• Update: legend to provide name to optgroup w3c/aria#2360

It might make sense to just allow the OpenUI explainer to our list of spec instead of waiting for all of these PRs to get merged and then to reference them all in the feature.

[captainbrosset]

@ddbeck I think we should merge this pretty much as is, allowing the OpenUI explainer URL. Customizable select has been in the works for many years, it needs to exist on our repo. We can use this as a guinea pig for early features if we want.