DB<1>  $foo = "a\nb\nc\n\nd\ne\n\n\nf\ng\nh\n\ni\n\n\nj\n"

  DB<2>  x $foo =~ /( (:? . | \n (?! \n\n) )+ ) /x
0  'a
b
c

d
e'
1  'e'