Today, I had a typo when I wrote =ISNUMBER(A2\). I expected Excel to complain, but it didn't - instead, it calculated the formula as if the backslash wasn't there. This works for some functions but not others. =COUNTIF(B:B,A2\) works, but =LEN(A2\) throws an error. It only seems to work for a range reference or name followed by a close-parenthesis for certain functions.
Why isn't Excel throwing an error here? Is there some functionality I'm not aware of, or some other purpose to this notation?