use XML::LibXML;

my $parser = XML::LibXML->new();
my $doc = $parser->parse_string( do{ local $/; <DATA> } );
for my $button ( $doc->findnodes("//button") ) {
    print "A button\n";
    for my $attr ( $button->attributes ) {
        printf "%30s --> %s\n", $attr->name, $attr->getValue;
    }
}

__DATA__
<?xml version="1.0" encoding="utf-8"?>
    <install type="module" version="1.0.0">
        <name>TEST</name>
        <notebook_tabs>
    <tab index="1">Create
        <button
    internal_name="test1"
    parent="-1"
    text="button 1"
    x_coordinate="5"
    y_coordinate="5"
    x_size="-1"
    y_size="-1"
    evt_1="EVT_BUTTON"
    evt_1_function="testclick" />

        <button
    internal_name="test2"
    parent="-1"
    text="button 2"
    x_coordinate="50"
    y_coordinate="50"
    x_size="-1"
    y_size="-1"
    evt_1="EVT_BUTTON"
    evt_1_function="testclick2" />

    </tab>
    <tab index="2">Assign</tab>
        </notebook_tabs>
    </install>