`<properties>` seems to be redundant with the popover API

[dead-claudia]

<properties> could be done in terms of native popovers: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Global_attributes/popover.

There's precedent already in <details> and slotted custom elements for giving one behavior for specific elements (<summary> and elements with slot attributes) while giving another behavior for the rest, so it's safe to just drop that IMHO. And notably, popovers have a complete separation of trigger element and popover element, so it won't even be necessary to have the popover in the <feature> at all.

[prushforth]

Yes, this is the subject of an investigation that we've been meaning to pursue, but have not yet had time to do so. Also, popover API didn't exist at the time we started this project, but you are correct we need to figure out how to incorporate it!