The docs start out with "as outlined in PEP 3119; see the PEP for why this was added to Python".  I think it would be a good doc enhancement request to extract the motivation and other description out of that pep and put it in the main docs in a suitable form, and make sure this point is included.  We used to just treat the peps as extensions of the documentation, but we've found over time that it is better to actually move the important parts of the text into the main docs, since the actual implementation and sometimes even how we talk about the feature tends to evolve away from the original PEP over time.