https://docs.python.org/3.6/library/idle.html starts with '25.5 IDLE'.
https://docs.python.org/3.7/library/idle.html starts with 'IDLE'.
The chapter and sections numbers are gone.

The current idlelib/help.html was copied (and stripped) from a Doc/build/library/idle.html built from the current Doc/library/idle.rst with Sphinx 1.7.4.  It was merged 2018 June 10.  See #33610.  Headers have chapter-section numbers.  (The chapter number is detected on the first line and removed from all headers before display.) 

When I changed idle.rst on a branch of master and rebuilt the docs with 1.7.4, there were over 100 warnings about an unknown doctest directive 'skipif'.  When I upgraded to Sphinx 1.8.1, the warnings disappeared, and so did the chapter-section numbers.  So it appears that the 3.7+ docs are meant to be built, and 3.7+ online docs are being built, with the newer Sphinx.  I am not sure of whether the loss of numbers is intentional and permanent, but for the present, I will use the 1.8 versions of idle.html and the derived help.html.  idlelib/help.html is currently the same for all of 3.6 to 3.8, so one diff can be merged and back-ported.

help.py is also the same for all 3 versions.  But the loss of numbers breaks it.  The upcoming patch will also fix this (but not immediately delete the code that handles numbers.  For the moment, I will replace the numbers in the Table of Contents with indents.