#!/usr/bin/perl
use strict;
use warnings;

use vars qw($strip $text);
$text = '';
for (<>) {
    /^(.*?<.> )([\w-]+|\S+)(.*?)$/ or next;
    my $level = length $1;
    my $op    = lc $2;
    my $pv    = (grep defined(), $3 =~ /[IN]V (\d+)|PV "((?:\\"|[^"])*)"/)[0];

    if ( not defined $strip ) {
        $strip = $level;
        $level = 0;
    } else {
        $level -= $strip;
        $level /= 3;
    }
    $text .= (" " x $level) . "$op@{[ defined $pv ? qq[ $pv] : '' ]}\n";
}
while ( $text =~ /^(\s*)(?:ex-|null).*/gm ) {
    my $pos      = $-[0];
    my $level = length $1;
    substr( $text, $pos ) =~ s/^(.*\n)// or next;
    substr( $text, $pos ) =~ /^\s{0,$level}\S/m or next;
    my $section = $-[0];
        substr( $text, $pos, $section ) =~ s/^ //gm;
}
continue {
    pos($text) = 0;
}
$text =~ s/ /   /g;
print $text;