Thanks Nicolas.
contrib/lisp/ox-gfm.el
54: :export-block '("GFM" "GITHUB FLAVORED MARKDOWN")
(Copied Lars for above)
contrib/lisp/ox-freemind.el
46: :export-block "FREEMIND"
(Copied Jambunathan for above)
(And copying you for groff and org.texi)
contrib/lisp/ox-groff.el
95: :export-block "GROFF"
doc/org.texi
17971:@code{:export-block} (to specify what blocks should not be exported by this
doc/org
16222:dispatcher), ‘:export-block’ (to specify what blocks should not be
etc/ORG-NEWS
78:Moreover, ~:export-block~ keyword used in ~org-export-define-backend~
Thanks.