> FTR there were a few actual errors that I fixed (mostly about bytes vs string).

Great!  Note that for the others, I was just trying to make the files parseable rather than passing.  Currently, doctest aborts out on the files I fixed without even attempting to run the examples.

> That can be done for 3.4+ only though.

Well, yes and no.  If there is a helper script to check documentation, it could be run on any branch regardless of whether the script is in source control.  For example, I was planning to write such a script (from the regrtest patch I put together before) to help me when checking people's patches to code snippets in the documentation.