Per the manner in which the summary element is exposed to Safari's Webkit (announced as "summary" but no matching ARIA role) and Blink (announced as and reported as a "DisclosureTriangle"role) these "buttons" are not discoverable when navigating by form controls or button elements with VoiceOver on macOS or iOS.

Additionally, due to poor support for aria-haspopup="dialog" these elements will be exposed as popup buttons for "menus", which, depending on the screen reader will inform a user certain keys will become available to them, which is not true.

I would suggest that role=button is added to the summary elements when JavaScript is enabled to better ensure these elements which are visually presented as buttons are also discoverable as the buttons they are meant to be.

Additionally, I would suggest that aria-haspopup=dialog is removed until it receives better support.