I see these in Documentation/Makefile:
#
# For asciidoc ...
# -7.1.2, no extra settings are needed.
# 8.0-, set ASCIIDOC8.
#
#
# For docbook-xsl ...
# -1.68.1, set ASCIIDOC_NO_ROFF? (based on changelog from 1.73.0)
# 1.69.0, no extra settings are needed?
# 1.69.1-1.71.0, set DOCBOOK_SUPPRESS_SP?
# 1.71.1, no extra settings are needed?
# 1.72.0, set DOCBOOK_XSL_172.
# 1.73.0-, set ASCIIDOC_NO_ROFF
#
#
# If you had been using DOCBOOK_XSL_172 in an attempt to get rid
# of 'the ".ft C" problem' in your generated manpages, and you
# instead ended up with weird characters around callouts, try
# using ASCIIDOC_NO_ROFF instead (it works fine with ASCIIDOC8).