Lately somewhere I heard an announcement on a train stop that sounded a bit wrong. Then I put some different words to fix it but now I feel unsure about all the alterations.
Please do not cross the yellow line till the train stops completely.
Please do not cross the yellow line until the train stops completely.
Please do not cross the yellow line before the train stops completely.
Which are right, which aren't, and why?
To me, only before sounds right but I can only say that because of instincts. Would like to know the right way. I tried looking for until-before differences but I couldn't relate any to this specific case.