>perl -wMstrict -le
"my @strings = qw(nowknow knownow know now no);
 ;;
 my $pattern1 = qr{  now }xms;
 my $pattern2 = qr{ know }xms;
 ;;
 my $regex1 = qr{ (?= \A .*? $pattern1) (?= \A .*? $pattern2) }xms;
 my $regex2 = qr{ $pattern1 $pattern2 | $pattern2 $pattern1   }xms;
 ;;
 for my $regex ($regex1, $regex2) {
   print qq{for regex $regex};
   for my $string (@strings) {
     print qq{  '$string' has },
           $string =~ $regex ? 'a' : 'NO',
           ' match';
     }
   }
"
for regex (?msx-i: (?= \A .*? (?msx-i:  now )) (?= \A .*? (?msx-i: know )) )
  'nowknow' has a match
  'knownow' has a match
  'know' has a match
  'now' has NO match
  'no' has NO match
for regex (?msx-i: (?msx-i:  now ) (?msx-i: know ) | (?msx-i: know ) (?msx-i:  now )   )
  'nowknow' has a match
  'knownow' has a match
  'know' has NO match
  'now' has NO match
  'no' has NO match