This proposal includes parser, styling, and rendering changes to make the <select> element fully customizable by authors.

Explainer: https://open-ui.org/components/customizableselect

Spec PR: #10548

Spec PRs (old):

• Relax <select> parser #10557
• Update content model for customizable select #10586
• Define base appearance for <select> #10629
• Define the <selectedcontent> element #10633
• Add UA stylesheet for <select> base appearance #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 and allowances for 'button' part of select w3c/html-aria#528
• Update: legend to provide name to optgroup w3c/aria#2360

Related HTML issues:

• Timing of cloning for the <selectedoption> element #10520
• Should datalist, option, object, and/or iframe elements be listed in "interactive content"? #10755
• How to spec user interaction for select #10762
• Is it ok for appearance:base <select> not to require user activation before showPicker()? #10604
• Selection in form control elements, user-select, and customizable select #10876
• Content model and 'what' to render for stylable <select> elements #10317
• HTML parser changes for customizable <select> #10310

Related CSS issues:

• [css-ui] Changing UA styles based on the computed value of the appearance property w3c/csswg-drafts#10028
• How to implement and shape API for <selectedoption> element for <select> w3c/csswg-drafts#10242
• [css-ui] New value(s) for the appearance property to support <select> stylability w3c/csswg-drafts#10333
• [css-ui] DOM/Box structure for appearance:base-select w3c/csswg-drafts#10380
• [css-ui] Pseudo-elements for stylable select w3c/csswg-drafts#10462
• [css-ui] Pseudo-element for select's UA button w3c/csswg-drafts#10717
• [css-ui] Pseudo-element for select's UA popover w3c/csswg-drafts#10758
• [css-forms-1] Should ::picker(select) match :popover-open? w3c/csswg-drafts#10775
• [css-ui] UA stylesheet for appearance:base <select> w3c/csswg-drafts#10857
• [css-ui] Pseudo-elements for checkmark and dropdown icon for appearance:base <select> w3c/csswg-drafts#10908
• [css-ui] Colors to use for appearance:base <select> w3c/csswg-drafts#10909
• [selectors-4] Should we have :open and :closed? w3c/csswg-drafts#11039
• [css-ui] select:hover and select:active styles w3c/csswg-drafts#11185

Standards positions:

• HTML selectedcontent element mozilla/standards-positions#1142
• Customizable select element mozilla/standards-positions#1060
• Relax <select> parser WebKit/standards-positions#414
• Relax <select> parser mozilla/standards-positions#1086
• Customizable select element WebKit/standards-positions#386