CommandEvent

<button commandfor="mypopover" command="show-popover">Show popover</button>
<div popover id="mypopover" role="[declare appropriate ARIA role]">
  <!-- popover content here -->
  <button commandfor="mypopover" command="hide-popover">Hide popover</button>
</div>

const popover = document.getElementById("mypopover");
// …
popover.addEventListener("command", (event) => {
  if (event.command === "show-popover") {
    console.log("Popover is about to be shown");
  }
});

<button commandfor="the-image" command="--rotate-left">Rotate Left</button>
<button commandfor="the-image" command="--rotate-right">Rotate Right</button>
<img id="the-image" src="photo.jpg" alt="[add appropriate alt text here]" />

const image = document.getElementById("the-image");
image.addEventListener("command", (event) => {
  if (event.command === "--rotate-left") {
    event.target.style.rotate = "-90deg";
  } else if (event.command === "--rotate-right") {
    event.target.style.rotate = "90deg";
  }
});