*click* ...a lightbulb turns on...

Thank you for the example code - that made all the difference! I didn't realize that $section was actually an XML::Twig::Elt object. Using your example as a starting point, I was able to get what I needed.

At first I thought I needed to parse the XML chunks into a data structure (such as that returned by XML::Simple), which I accomplished using 

my $struct = $section->simplify( forcearray => 1 );

[download]
but I soon realized that was overkill for what I really needed - the value of the attributes for the class (etc) tags. The $elt->att( $attribute ) method did the trick. An example of the class handler from my working code is below. 
sub uml_class
{
    my ( $twig, $section ) = @_;

    print "data for class:\n";
    print "   name = ", $section->att( 'name' ), "\n";
    print "   xmi.id = ", $section->att( 'xmi.id' ), "\n";

    my $subTwig = XML::Twig->new( twig_roots => {
                                      'UML:Attribute' => \&uml_attr } 
+);
    # $subTwig->parse( $xml ); # original code (typo)
    $subTwig->parse( $section->sprint() );
}

[download]

Thanks again! I knew I was making it too hard. :-)

Update: corrected typo in the example code

In reply to Re^2: Pulling out sections of an XMI file with XML::Twig by bobf
in thread Pulling out sections of an XMI file with XML::Twig by bobf

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