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It's a regular expression match, actually. �The standard matcher ignores everything between the Traceback line (matched by a regex) and the first unindented line that follows in the doctest. �However, if you explicitly try to match a traceback with the ellipsis matcher, intending to observe whether certain specific lines are printed, then you wouldn't be using doctest's built-in matcher, and that was the case I was concerned about.

However, as it turns out, I was confused about when this latter case occurs: in order to do it, you have to actually intentionally print a traceback (e.g. via traceback.format\_exception() and friends), rather than allowing the exception to propagate normally. �This doesn't happen nearly as often in my doctests as I thought it did, but if format\_exception() changes it'll still affect some people.

The other piece I was pointing out was that if you change the message without changing the doctest regex, then pasting an interpreter transcript into a doctest will no longer work, because doctest will think it's trying to match non-error output. �So that has to be changed when the exception format changes.

So, no actual objection here; just saying that if you don't change that regex, people who create \*new\* doctests with tracebacks won't be able to get them to work without deleting the version info from their copy-pasted tracebacks. �I was also concerned about a situation that, while it exists, does not occur anywhere near as frequently as I thought it would in my own tests, even for things that seriously abuse Python internals and likely can't be ported to Python 3 anyway. �;-)