I then considered the difference to 'n' too miniscule to bother with it.
is perl5db.pl required to be backward compatible to Perl 4.x
Well of course not. It uses lexical variables for starters. You are looking at possibly the oldest, continually tweaked file in the Perl distribution though. It has enough cruft and differing code styles and idioms without adding one more.
• another intruder with the mooring in the heart of the Perl