Default Windows UI elements determine hotkeys by marking the hotkey character (Alt + ...) with an &
.
For examble, in your case the UI text will most likely be something like &Accept
and &Don't accept
, which would result in the A and D being shown underlined and the shortcuts Alt + A and Alt + D being assigned. It doesn't have to be the very first character in a string, so something like C&ancel
will work as well.
If there are multiple elements with the same hotkey, using the key combination allows you to switch between these elements (similar to how Tab works).
However, depending on system settings, it's possible to hide those shortcuts by default (got introduced some time in the Windows 98 days I think). They'll only appear once you hit Alt by default, which may be changed under Ease of Access -> Keyboard in Control Panel.