As part of #30777, Cheryl Sabella listed Variables defined for a tab page, and the use thereof, in the docstring for the tab page.  This revealed some anomalies.

Duplicate: font_name is defined on font and highlight pages.  The first StringVariable should be attached to a widget before the name is rebound.  We should investigate after there are tests for the two pages.

Unused: for anything deleted, make sure that there is no corresponding trace function left.

binding_target (keys) sounds like something that was never an external option but just an internal implementation detail; delete.

encoding (general) *is* an external option, but I believe used only by 2.x.  Recheck (in config.py also) and probably delete.

user_help_browser and help_browser (general) may have once been options.  We now use the system browser, which, at least on some systems, users can set.  Delete.

Created the pull request so it's ready once the tests are available.

After wresting with a test for #30870, I am not sure we will ever have the full tests I would like.  Anyway, I concluded that the replacement of font_name is a bug.  It did not matter because all pages are created before configuration is read.  If any of font_name, font_bold, or font_size are changed, set_font_sample is called to define a new font and reset the fonts for the samples on both font and hightlight pages.  I checked that this still works.

I convinced myself that the 3.6+ dialog cannot change 'encoding' in userCfg.

New changeset aa8d0a24694bea05061f1920ec3f944a9e6799d5 by terryjreedy (csabella) in branch 'master':
bpo-30851: IDLE: Remove unused tk variables in configdialog. (#2626)
https://github.com/python/cpython/commit/aa8d0a24694bea05061f1920ec3f944a9e6799d5

New changeset 8e3f73e5499a5bc575a5e7ad4ee0f16b1aaae829 by terryjreedy in branch '3.6':
[3.6] bpo-30851: IDLE: Remove unused tk variables in configdialog. (GH-2626) (#2648)
https://github.com/python/cpython/commit/8e3f73e5499a5bc575a5e7ad4ee0f16b1aaae829