I found your approach with a depth variable a bit hard to follow.

I find it's easier to think in terms of "what list am I adding into currently?", and "what's the stack of lists I was adding to?". That 2nd question handles the possibility that start/end blocks are nested.

So here's what I came up with (but see jethro's answer below, his is much cleaner):

#!/usr/local/bin/perl

use strict;
use warnings;

use Data::Dumper;
$Data::Dumper::Indent = 1;

my @lines = <DATA>;
chomp @lines;

my @list = ([q{div}, {id => q{article}}]);
my $currentList_r = \@{$list[0]};
my $currentDiv="";

my @listStack;

LINE:
for my $line (@lines){
    chomp $line;
    if($line=~/^;([^;]+)_start;$/) {
        $currentDiv=$1;
        my $divList_r=['div',{class=>$1}];
        push @listStack, $currentList_r;
        $currentList_r=$divList_r;
        next LINE;
    }

    if($line=~/^;([^;]+)_end;$/) {
        die "Tag mismatch between start ($currentDiv) and end ($1)"
            unless $1 eq $currentDiv;
        $currentDiv="";
        die "end with no matching start!" unless scalar @listStack;
        push @{$listStack[-1]}, $currentList_r;
        $currentList_r = pop @listStack;
        next LINE;
    }

    my ($tag, $txt) = $line =~ /^;([^;]+);(.*)/;

    push @{$currentList_r}, [$tag, $txt];

}

print Dumper(\@list),

__DATA__
;p;one
;greybox_start;
;h2;two
;greybox_end;
;p;three
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