GUI scripting method for toggling options (without using the mouse)

is there any way to choose between the (format: (web archive) / (source)) in the safari save as menu. I’m looking for something similar to the methods you used for menu bar actions. How do you discover these? (Using mouseclicks with automator works, but I want a more robust method.)

obviously, I should use tab keys to focus on the menu :facepalm: