hypothesis:
                  $re1 <= $re2
is_less_or_equal( $re1,   $re2 )
      specific -> $re1    $re2 <- generic

if exists $str that
$str =~ /$re1/ and $str =~ /$re2/ -> no consequence
$str =~ /$re1/ and $str !~ /$re2/ -> falsifies hypothesis
$str !~ /$re1/ and $str =~ /$re2/ -> corroborates hypothesis
$str !~ /$re1/ and $str !~ /$re2/ -> no consequence