I'd use something simpler for parsing the XML than XML::Simple, like XML::Parser, although I don't know what you want the final output for so the rendering below may not suit you:

use warnings;
use strict;
use XML::Parser;

my $xmlStr = <<XML;
<A>
    <B>
        <C>
            <element type="k" name="p" online="yes"/>
            <element type="i" name="e" online="yes"/>
        </C>
        <D>
            <element type="kd" name="pd" online="no"/>
            <element type="id" name="ed" online="yes"/>
            <element type="yd" name="zd" online="no"/>
        </D>
    </B>
    <Z>
        <C>
            <element type="k" name="z" online="yes"/>
            <element type="t" name="p" online="yes"/>
        </C>
        <E>
            <element type="kd" name="pd" online="no"/>
            <element type="id" name="ed" online="yes"/>
        </E>

    </Z>
</A>
XML

use constant kIndentSize => 4;

my $indent = '';
my $xs1 = XML::Parser->new (
    Handlers => {
        Start => sub {start (\$indent, @_);},
        End   => sub {end (\$indent, @_);},
        Char  => sub {char (\$indent, @_);}
    });

$xs1->parse ($xmlStr);


sub start {
    my ($indent, $expat, $element, %attr) = @_;

    print "$$indent$element\n";
    $$indent .= ' ' x kIndentSize;
    print "$$indent$_ : $attr{$_}\n" for sort keys %attr;
    return;
}

sub end {
    my ($indent, $expat, $element) = @_;

    substr $$indent, -(kIndentSize), kIndentSize, '';
    return;
}

sub char {
    my ($indent, $expat, $string) = @_;

    chomp $string;
    $string =~ s/^\s+|\s+$//g;
    return unless length $string;

    print "$$indent$string\n";
    return;
}
[download]

Prints:

A
    B
        C
            element
                name : p
                online : yes
                type : k
            element
                name : e
                online : yes
                type : i
        D
            element
                name : pd
                online : no
                type : kd
            element
                name : ed
                online : yes
                type : id
            element
                name : zd
                online : no
                type : yd
    Z
        C
            element
                name : z
                online : yes
                type : k
            element
                name : p
                online : yes
                type : t
        E
            element
                name : pd
                online : no
                type : kd
            element
                name : ed
                online : yes
                type : id
[download]