One of the nice features of the Popover API is its light dismiss behavior. This chromestatus is about bringing that same capability to `<dialog>`. A new `closedby` attribute controls behavior: `<dialog closedby=none>` - no user-triggered closing of dialogs at all. `<dialog closedby=closerequest>` - user pressing ESC (or other close trigger) closes the dialog `<dialog closedby=any>` - user clicking outside the dialog, or pressing ESC, closes the dialog. Akin to `popover=auto` behavior.
Developers sometimes would like dialog elements to exhibit "light dismiss" behavior, similar to the behavior popovers get by default. Previously, this required JS-based click handlers on the dialog and awkward logic. This feature provides easy light dismiss functionality via a declarative attribute.