# $Id: Tree.pm,v 1.2 2003-07-31 07:54:51 matt Exp $

package XML::Parser::Style::Tree;
use strict;

sub Init {
    my $expat = shift;
    $expat->{Lists} = [];
    $expat->{Curlist} = $expat->{Tree} = [];
}

sub Start {
    my $expat   = shift;
    my $tag     = shift;
    my $newlist = [ {@_} ];
    push @{ $expat->{Lists} }, $expat->{Curlist};
    push @{ $expat->{Curlist} }, $tag => $newlist;
    $expat->{Curlist} = $newlist;
}

sub End {
    my $expat = shift;
    my $tag   = shift;
    $expat->{Curlist} = pop @{ $expat->{Lists} };
}

sub Char {
    my $expat = shift;
    my $text  = shift;
    my $clist = $expat->{Curlist};
    my $pos   = $#$clist;

    if ( $pos > 0 and $clist->[ $pos - 1 ] eq '0' ) {
        $clist->[$pos] .= $text;
    }
    else {
        push @$clist, 0 => $text;
    }
}

sub Final {
    my $expat = shift;
    delete $expat->{Curlist};
    delete $expat->{Lists};
    $expat->{Tree};
}

1;
__END__

=head1 NAME

XML::Parser::Style::Tree - Tree style parser

=head1 SYNOPSIS

  use XML::Parser;
  my $p = XML::Parser->new(Style => 'Tree');
  my $tree = $p->parsefile('foo.xml');

=head1 DESCRIPTION

This module implements XML::Parser's Tree style parser.

When parsing a document, C<parse()> will return a parse tree for the
document. Each node in the tree
takes the form of a tag, content pair. Text nodes are represented with
a pseudo-tag of "0" and the string that is their content. For elements,
the content is an array reference. The first item in the array is a
(possibly empty) hash reference containing attributes. The remainder of
the array is a sequence of tag-content pairs representing the content
of the element.

So for example the result of parsing:

  <foo><head id="a">Hello <em>there</em></head><bar>Howdy<ref/></bar>do</foo>

would be:

             Tag   Content
  ==================================================================
  [foo, [{}, head, [{id => "a"}, 0, "Hello ",  em, [{}, 0, "there"]],
              bar, [         {}, 0, "Howdy",  ref, [{}]],
                0, "do"
        ]
  ]

The root document "foo", has 3 children: a "head" element, a "bar"
element and the text "do". After the empty attribute hash, these are
represented in it's contents by 3 tag-content pairs.

=head2 Entity Expansion

The underlying Expat parser always expands predefined XML entity
references (C<&lt;>, C<&gt;>, C<&amp;>, C<&quot;>, C<&apos;>) in both
text content and attribute values before they reach the Tree style
handlers. This is required by the XML specification and cannot be
prevented. For example, C<&lt;> in the source XML will appear as C<< < >>
in the resulting tree structure.

If you need access to the original unexpanded text, consider using the
handler-based API with the C<original_string> method on the Expat object
instead of the Tree style.

=cut
