[css-anchor-1] Allow anchoring to popover invoker

[jpzwarte]

Use case: you have a <table> with N rows and you want to use a single popover element for all rows in the table.

<div id="popover" popover>...</div>

<tr>
  <td>
    <button popovertarget="popover" popovertargetaction="show"></button>
  </td>
</tr>
<tr>
  <td>
    <button popovertarget="popover" popovertargetaction="show"></button>
  </td>
</tr>
<!-- etc -->

Afaics you currently have to be explicit in the anchor name. So this scenario is not possible without the use of JS?

[tabatkins]

This is already possible via the implicit anchor element - in fact, Popover is currently the only thing that can set an implicit anchor.

So in this case the div could write something like #popover:popover-open { position: fixed; top: anchor(bottom); } and it would attach to the whichever button invoked it.