DB<106> $s='abc'
 => "abc"
 
  DB<107> $r=qr/abc/
 => qr/abc/
 
  DB<108> ref $r eq 'Regexp'
 => 1
 
  DB<109> ref $s eq 'Regexp'
 => ""
  
  DB<110> 'xabcx'=~m/$r/
 => 1
 
  DB<111> 'xabcx'=~m/$s/
 => 1