> * Drop notice of unsafe mode as "old" behavior; it's over 20 years old.
I wonder if "old" here was intended to contrast with AT&T troff behavior, which was to always run in what groff considers unsafe mode (in that it had no such distinction). Safer mode being a groff innovation does not seem well documented elsewhere: the Texinfo manual doesn't mention it, and groff_diff(7) covers only input and output differences, not invocation differences. (groff_diff(7) mentions the \n[.U] register but nothing else regarding this mode.) So I wonder if it's worth keeping the distinction here, though perhaps terming it "historical" or "traditional" rather than "old" behavior.
