This will predeclare all the subroutine whose names are
in the list, allowing you to use them without parentheses
even before theyre declared.
Unlike pragmas that affect the $^H hints variable, the use vars and
use subs declarations are not BLOCK-scoped. They are thus effective
for the entire package in which they appear. You may not rescind such
declarations with no vars or no subs.
See Pragmatic Modules in perlmodlib and strict subs in strict.