All reports of alternatively-build-depends-on-python-sphinx-and-python3-sphinx for the archive. The extended description of this tag is:
This package alternatively Build-Depends on the Python 2 or Python 3 version of the Sphinx documentation generator.
The 2.x series of Python is due for deprecation and will not be maintained by upstream past 2020 and will likely be dropped after the release of Debian "buster".
Please replace the alternative with a single build dependency on python3-sphinx.
This tag has not been emitted in any package tested by Lintian.