Toggle, add or remove a class — the three actions that compose with the element's own CSS.

The class lands on the element the click points at, which is the same handle MishkaCmsCore.Runtime.PageBuilder.ElementCss keys a rule on. One identity, two features: toggle is-open here and write &.is-open { … } in the CSS box, and that is an accordion with no code in it.

All three are client actions: Phoenix.LiveView.JS moves the class in the browser with no round trip, and the command survives a patch because it is part of what the server rendered.