Programming Perl, 3rd Edition

use less

use less;               # These are all UNIMPLEMENTED!

use less 'CPU';
use less 'memory';
use less 'time';
use less 'disk';
use less 'fat';         # great with "use locale";

Currently unimplemented, this pragma is intended to someday give hints to the compiler, code-generator, or interpreter to enable certain trade-offs.

It is not an error to ask to use less of something that Perl doesn't know how to make less of right now.