Relax <select> parser

[josepharhar]

Request for Mozilla Position on an Emerging Web Specification

• Specification title: Relax <select> parser
• Specification or proposal URL (if available): Relax <select> parser whatwg/html#10557
• Explainer URL (if available): https://open-ui.org/components/customizableselect/
• Proposal author(s) (@-mention GitHub accounts): @josepharhar
• Caniuse.com URL (optional):
• Bugzilla URL (optional):
• Mozillians who can provide input (optional):
• WebKit standards-position: Relax <select> parser WebKit/standards-positions#414

Other information

whatwg/html#10310 (comment)

[zcorpan]

Per whatwg/html#10310 (comment) the web compat situation needs more clarity. But a parser change is needed here in order to support other elements in a custom select, and the direction proposed here seems like the best for web developers long-term.

I reviewed the security risk of this change in whatwg/html#10310 (comment)

Conclusion: sanitizers need to have general protection against mXSS, and so this change doesn't introduce new mXSS vectors, even though the parsed tree can be very different between new and legacy parsers.

I suggest position: positive.

@hsivonen should sign off here before setting a position label.