DB<3> $r="abc|xyz";

  DB<4> $rx=qr($r);

  DB<5> p $rx
(?^u:abc|xyz)

##</code><code>##

  DB<6> $rx=qr(/$r/i);   # strike it, see update

  DB<7> p $rx
(?^u:/abc|xyz/i)

##</code><code>##

  DB<27> $rx = qr($r)i;    # or traditionally qr/$r/i

  DB<28> p $rx
(?^ui:abc|xyz)
  DB<29> p "XYZ" =~ $rx
1