about the property list (applicable form events) for 3D button object
when you create a 3D button with the popup arrow “none”, the on alternative click event is masked (in the “all” view).
when you select “separated” or “linked”, it remains masked in the “all” view, but by triggering an update of the property list, by re-selecting the button or by toggling views in the property list or by simply moving 4D away from frontmost, you’d see that event is available. it is simply an update issue of the property list.
as for handling the event at the form level, you are right, only the classic click/double click events are available. I can only guess why. perhaps it was an omission when the events were introduced in v2004. perhaps it is intentional to separate generic click events from context specific click events (header, long, alternative).
after all, the popup menu property is nothing more than a cosmetic feature. you have to call dynamic popup menu explicitly. if there is no need to make the distinction between a regular click and an alternative click, and you are only interested in displaying the small arrow, I agree, you have more control using the on clicked event and handle the cosmetic aspect yourself.