# I need a better way to phrase this. Ideas?
$BIGGER_REGEX = qr/ ... /; # The contents of qr// are a constant expression so are compiled at compile-time.

sub do_it_again {
    if ( $sexpert =~ $BIGGER_REGEX ) {
        ...
    }
}

do_it_again(); # the pre-compiled regex is used directly.
do_it_again(); # ditto

# This qr// was compiled a compile-time. Store a copy in $BIGGER_REGEX. No recompilation
# occurs now.
$BIGGER_REGEX = qr/ !!! /; 
do_it_again(); # Like before, a pre-compiled regex is used directly. Nothing special happens.