@Richard *******
it has to be what ever the immigration officer at passport control says it needs to be 😮
I have had reports of people standing at the stamp in counter be told by passport control that if they didn't show a ticket back to the country their passport is from within the days they would stamp in for they'd be denied entry.
Those people had to book flights back to their home country right then and there 😕
Now I will agree with you that at a land crossing it is highly unlikely IF a person is asked for onward travel that passport control would insist on return to country of origin