Opinion poll!

You have a <button>, it makes a <foo> open. What would be the best declarative attribute for the button to control the foo?

<button clickaction=open
17.1%
<button invokeaction=open
42.1%
<button command=open
26.3%
Other (comment ideas)
14.5%
Poll ended at .
@keithamus I'm all for writing valid html, so I'd always prefix custom attributes with data-. This use case can now oftentimes be addressed with standard popover markup. If you need to customize that, I'd do exactly that, if the behavior close enough.
https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/popover
If your use case is more in line with opening an accordion, there's the summary/details markup.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/summary
You can customize all that (e.g. with custom built in elements), but try avoiding reinventing the wheel.
popover - HTML: HyperText Markup Language | MDN

The popover global attribute is used to designate an element as a popover element.

MDN Web Docs
@keithamus Sorry, I may have missed the point, that you are discussing a possible standard here, not some framework of your's. In this case, please forgive me for my smartassing about "data-" and possibly other remarks (haven't thought that through).
@schrotie I appreciate the sentiment, I want to just use the platform too! Here's hoping we can make the platform even more usable 😉