> Doc/tools/extensions/suspicious.py is a CPython specific extension, it's not part of Sphinx. Maybe someone should open a feature request on Sphinx to get a similar feature without false positives (or at least less false positives).

This extension was written by Gabriel Genellina in 2009 when he discovered that:

   Several documents contain invalid reST markup that "leaks"
   into the html output (missing ``, incorrect indentation, etc.)

Extension added in bpo-4811 with:

commit 700cf28f410521066f40671f1da7db0302d753fd
Author: Georg Brandl <georg@python.org>
Date:   Sun Jan 4 10:23:49 2009 +0000

    Add "suspicious" builder which finds leftover markup in the HTML files.
    
    Patch by Gabriel Genellina.


The code didn't evolved much since it was added in 2009. Main changes.

commit 144c269cc8b82ab3b877797e1c7c26b0849e2b56
Author: Ezio Melotti <ezio.melotti@gmail.com>
Date:   Thu Mar 28 18:01:11 2013 +0200

    Update the suspicious builder to detect unused rules, and remove currently unusued rules.

bpo-22537:

commit 14b5a4da2732d3464c6b40527458005ccf19f95c
Author: Georg Brandl <georg@python.org>
Date:   Thu Oct 2 08:26:26 2014 +0200

    Closes #22537: Make sphinx extensions compatible with Python 2 or 3, like in the 3.x branches

Filename renamed:

* master: Doc/tools/extensions/suspicious.py
* Commit 160cbce92adc3ccbe4ae6e231ea27fb5ff28dca9 renames Doc/tools/suspicious.py to Doc/tools/extensions/suspicious.py
* Commit f16fbf940fdaec594eb1f4c5f9c61e926db53c5d renames Doc/tools/sphinxext/suspicious.py to  Doc/tools/suspicious.py