something like (just off my head; prob. needs work):

while (<>) {
   chomp if (my $num= /^DESCRIPTION$/ .. /^ENDDESCRIPTION/);
   next if $num==0 || $num =~ /E/;  # skip endpoints
   print;
   }
[download]

There was a thread on that a short time ago. Look up Range Operator in Perlop, and do a super search on flip-flop and variations for the past couple weeks.

—John