package MyHandler;

sub new { bless { indent => 0 }, shift }

sub handle_start {
  my ($self, $p, $el, %atts) = @_;
  # use $self->{indent} here
  ...
}

sub handle_end {
  my ($self) = @_;
  # likewise here
  ...
}

1;

...

use XML::Parser;
use strict;

sub parse_stuff {
  my $handler = MyHandler->new();
  my $parser = new XML::Parser(Handlers => { Start => sub { $handler->handle_start(@_) }, 
      End => sub { $handler->handle_end(@_)});

  $parser->parsefile('/tmp/ra.xml');
}