
Perl adds new features all the time
- new operators
  // (5.10)

since 5.10 we have the feature pragma,
which allows backwards compatibility

the main goal is that you can upgrade your perl binary
and should need to modify any (sensibly written) perl scripts that 
worked under an earlier version of Perl

Perl has a time machine

line 0 - code like it's 2002!
line 1 - use v5.36, it's now 2022!
