string=<\n\n>
   no modifier: regex=/$\n\n/
     no match => $ needs m modifier to match internal nl
   m modifier (multi line mode): regex=/$\n\n/m
     match => $ needs m modifier to match internal nl
string=<\n\n>
   no modifier: regex=/\n$\n/
     match => $ matches final nl after internal nl
   m modifier (multi line mode): regex=/\n$\n/m
     match => $ matches final nl after internal nl
string=<\n\n>
   no modifier: regex=/\n\n/
     match => 
   m modifier (multi line mode): regex=/\n\n/m
     match =>