Standardized by the Open UI group. Adds command and commandfor attributes to buttons so native behaviors (like opening a dialog as a modal) fire without writing click handlers. Currently native commands cover the dialog element, with planned expansion to video play/pause, number field increment/decrement, menus, burger menus, cookie banners, sliding drawers, etc. Custom commands (prefixed with --) let apps remove click-handler boilerplate and just listen for command events on a target element. Shipping in all current browsers with a small polyfill available for legacy support.