In conformance with the recommendations of the Graphviz team, in the next
version Bison the option
--graphwill generate a *.gv file by default,
instead of *.dot. A transition started in Bison 3.4.
I thought this was interesting because (1) I had no idea Bison could generate Graphviz and (2) I did not realize .gv was preferred over .dot. Maybe these are widely known to others.