my @beginnings =
( qr{This is valid</a>},
  qr{[So]+(?:IS|isnt) this}, 
);

my @endings =
( qr{(?:we) Should not [be] [Pp]arsing after},
  qr{either (o|f) these [Ll]ines},
);

sub isbeg {
  my $test = shift;
  foreach (@beginnings) { return undef unless $test =~ $_ }
  $test;
}

sub isend {
  my $test = shift;
  foreach (@endings) { return undef unless $test =~ $_}
  $test;
}

# here is the part I dislike, partially because of the $parsing variable
# it just doesnt seem as "clean" as something some of
# you would write.

  my $parsing;
  foreach my $line (@lines) {
    $parsing++ if isbeg( $line );
    push @extracted, "$line\n" if $parsing;
    last if isend( $line );
  }