The traceback module formats several edge cases of SyntaxError different than CPython's default formatting.

- There's an off-by-one error if the column offset (printed as a caret) points past the last character (example: 'a +='). The clipping is wrong and the caret points to the last character.

- If the offset is <= 0, it appears the code silently adds the length of the source text.

- The system formatting suppresses the caret if the offset is -1; the only way to suppress the caret with the traceback module is setting the offset to None (or setting the source text to None).

- The system formatting can position the caret way past the end of the source text; the traceback module clips (also see the first bullet).

I propose to make the traceback module behave the same way as the system module in all cases. I also propose to make both suppress the caret if the offset is <= 0. Finally I propose to make the system formatting limit the offset to just past the end of the source text.

I propose not to bother changing anything in 3.8 or before.