To answer my own question regarding merging/expanding elements, here is a snippet on how to do it with sax: 

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

    use base qw(XML::SAX::Base);
    use Data::Dumper;

    use XML::SAX::ParserFactory;
    use XML::SAX::Writer;

    sub start_element {
        my $self = shift;
        my $data = shift;

        if( $data->{LocalName} eq 'expand') {
            $self->{in_include}++;
            my $p = XML::SAX::ParserFactory->parser( Handler => $self 
+);
            $p->parse_string( "<expanded>This is my expanded tag</expa
+nded>" );
            return;
        }
     
        #$data->{Attributes} = undef;
        $self->SUPER::start_element($data);
        #print Dumper($data); 
    }

    sub characters {
        my $self = shift;
        my $data = shift;
        
        #print "Data is $data->{Data}" if defined $data->{Data}; 
        $self->SUPER::characters($data);
    }

    sub end_element {
        my ($self, $element) = @_;
        if ($element->{LocalName} eq "expand") {
            $self->{in_include}--;
        } else {
            $self->SUPER::end_element($element);
        }
    }

    sub start_document { # same for end_document
        my($self, $data) = @_;
        return if($self->{in_include});
        $self->SUPER::start_document($data);
    }

    sub end_document { # same for end_document
        my($self, $data) = @_;
        return if($self->{in_include});
        $self->SUPER::end_document($data);
    }

    1;

    #============================
    #Main programm
    #============================
    use strict;
    use warnings;

    use XML::SAX::ParserFactory;
    use XML::SAX::Writer;

    my $out;

    my $o = XML::SAX::Writer->new( Output => \$out );
    my $h = MyHandler->new( Handler => $o );
    my $p = XML::SAX::ParserFactory->parser(Handler => $h);

    my $data;
    { local undef $/ }; $data = <DATA>;
    $p->parse_string( $data );
    print $out;


    __DATA__
    <?xml version="1.0" encoding="UTF-8"?>
    <html xmlns="http://www.w3.org/1999/xhtml" xmlns:wicket="http://wi
+cket.apache.org/dtds.data/wicket-xhtml1.4-strict.dtd">
    <body>
    <wicket:panel>
        <form wicket:id="mvpForm">
            <span>Edit Information: </span>
            <input type="checkbox" wicket:id="editForm"/>

            <span>Name: </span>
            <span wicket:id="name"></span>
            <input type="text" wicket:id="nameEdit"/>
                                    
            <span>Last Name: </span>
            <span wicket:id="lastName"></span>
            <input type="text" wicket:id="lastNameEdit"/>
                                    
            <span>DOB: </span>
            <span wicket:id="dob"></span>
            <input type="text" wicket:id="dobEdit"/>
                                    
            <span>Occupation: </span>
            <span wicket:id="occupation"></span>
            <input type="text" wicket:id="occupationEdit"/>
                                    
            <span>Gender: </span>
            <span wicket:id="gender"></span>
            <span wicket:id="genderEdit"/>
                                    
            <input type="submit" wicket:id="submit"/>
        
            <expand/>
            
        </form>
    </wicket:panel>
    </body>
    </html>

[download]

The `<expand/>` tag will be replaced by `<expanded>This is my expanded tag</expanded>`.

Basically all is needed is to create a new parser and hand it a file/string to be parsed. However, note that there are a couple of gotchas. The first one is to stop propagating the event where you have intercepted the tag to be expanded. In other words don't call $self->SUPER::start/end_element whenever expanding/nesting tags, that will prevent the replaced tag to end up in the output. Second, it's required to intercept start_document/end_document and skip calling the parent for those ones, otherwise the following error will be produced:

>Trying to pop context without push context at /usr/share/perl5/XML/NamespaceSupport.pm line 79, <DATA> chunk 1.

In other words some clean up fails:

>This message is being triggered because XML::NamespaceSupport does some initialisation on a start_document event and some cleanup on an end_document event. The problem is that with your code there will be a pair of these events for the main document and a nested pair for each included document. When the second end_document event occurs, there is nothing to clean up - hence the message.

Taken from here

In reply to Re^2: Using Perl XML::SAX to modify XML documents by dryajov
in thread Using Perl XML::SAX to modify XML documents by dryajov

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