while (<>) {
   if    ( /^Heading Here:/    ) { $_ = "\n" . $_; $indent = 1; }
   elsif ( /^Another Heading:/ ) { $indent = 1; }
   elsif ( /^End of section:/  ) { $indent = 0; }
   elsif ( $indent             ) { $_ = "  " . $_; }

   print;
}