BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Sabre//Sabre VObject 4.5.8//EN CALSCALE:GREGORIAN LAST-MODIFIED:20260219T060920Z BEGIN:VTIMEZONE TZID:Asia/Tokyo X-MICROSOFT-CDO-TZID:20 BEGIN:STANDARD DTSTART:20241117T071500 TZOFFSETFROM:+0900 TZOFFSETTO:+0900 TZNAME:JST END:STANDARD END:VTIMEZONE BEGIN:VEVENT UID:e3553cb1-34f7-47f5-81e8-eea4da37aa73 DTSTAMP:20260219T060920Z SUMMARY:Custom attributes for all elements DTSTART;TZID=Asia/Tokyo:20251112T161500 DTEND;TZID=Asia/Tokyo:20251112T171500 DESCRIPTION:https://www.w3.org/events/meetings/e3553cb1-34f7-47f5-81e8-eea4 da37aa73/\n\n2023's breakouts had a [discussion on alternatives to customi zed built-ins](https://github.com/w3c/tpac2023-breakouts/issues/44).\n\nA sketch of a proposal came out around this time: customised attributes. htt ps://github.com/WICG/webcomponents/issues/1029\n\nI'd like to set some tim e to discuss this idea\, the merits\, complexities\, and discuss whether o r not this solves problems for developers without too much complexity for the platform.\n\n**Goal(s):**\nDecide if a model for Custom Attributes is viable in the platform\, and what a design might look like.\n\nAgenda\n\n1 . Can we reasonably enforce that HTML will only standardise attribute name s without dashes\, and developers can use dashes (modulo `data-*` and `ari a-*`)\; see https://github.com/whatwg/html/issues/2271\n2. Can we agree th at pursuing a series of lifecycle callbacks for when an attribute node is connected\, disconnected\, and changed would be a useful feature for devel opers\, and something that the major browser vendors would be happy pursui ng.\n3. Do we agree that `class CustomAttr extends Attr {}` is a good desi gn choice? This means giving Attr() a constructor\, and would be `getAttri buteNode()` etc could now return subclasses of `Attr`. It would also mean `setAttribute`/`removeAttribute`/`toggleAttribute` would run these lifecyc les\, including: looking up the attribute name in some form of registry\, & calling into script. Is this okay?\n4. Can Attrs leverage `CEReactions` or would we need some kind of new `CAReactions`?\n5. Reflection is useful for attributes\, could we design a way to bake reflection into custom attr ibute nodes? E.g. `static reflectedAs = "long"` which would change the beh aviour of `Attr.prototype.value` for such custom attributes.\n6. Default v alues for attributes is useful\, can we design something like `static defa ultValue = ...`?\n7. We would likely need some kind of attribute registry (much like `window.customElements`). Does `window.customAttributes` make s ense? Perhaps we wish to define attributes only for specific elements\, su ch as `