That's already not true for Quoted entries that contain the separator. Which I think is a common CSV use case. But I do agree you could have a heuristic. E.g.

That's already not true for Quoted entries that contain the separator. Which I think is a common CSV use case. But I do agree you could have a heuristic. E.g. ends in .csv and contains a lot more commas/semicolons/tabs than you would expect in normal text in the first 1-5 lines. You could still have the flag as a fallback when you need something that's completely reliable.