I am still trying to wrap my head around XML::Twig and I could really use a nudge in the right direction. The docs just aren't making it through the fog and into my head today.

I am trying to parse an XMI file that has the following overall structure (greatly simplified, of course): 

    <XMI xmlns:UML="omg.org/UML1.3" xmi.version="1.1" timestamp="2007-
+06-26...">
      <XMI.content>
    
            <UML:Class name="Address" xmi.id="EAID_009DB5F9_3A9D_44d0_
+88BD_...">
              <UML:ModelElement.taggedValue>
                <UML:TaggedValue tag="isSpecification" value="false" /
+>
                <UML:TaggedValue tag="ea_stype" value="Class" />
              </UML:ModelElement.taggedValue>
              <UML:Classifier.feature>
                <UML:Attribute name="city" changeable="none" >
                  <UML:ModelElement.taggedValue>
                    <UML:TaggedValue tag="description" value="City" />
                    <UML:TaggedValue tag="ea_guid" xmi.id="EAID_661614
+4D_..." />
                  </UML:ModelElement.taggedValue>
                </UML:Attribute>
              </UML:Classifier.feature>
            </UML:Class>
    
        <UML:TaggedValue
            tag="created"
            xmi.id="EAID_17DA671B_9257_42f1_8AA8_0EF5F305DBD0"
            modelElement="EAID_31EB028E_30B2_430a_9168_1010A2A7B851" /
+>
        <UML:TaggedValue
            tag="ea_stype"
            xmi.id="EAID_FAF2F308_9EB4_4f83_90F6_BE8ABC10087C"
            modelElement="EAID_31EB028E_30B2_430a_9168_1010A2A7B851" /
+>
    
      </XMI.content>
    </XMI>

[download]

The handlers I created are as follows: 

        my $twig =
            XML::Twig->new(
                start_tag_handlers => {
                        'UML:Class' => \&uml_class_start,
                        'UML:Package' => \&uml_package_start,
                },
                twig_handlers => {
                        # purge at the end of each class section
                        'UML:Class' => sub { $_[0]->purge },
                        'UML:Attribute' => \&uml_attribute,
                        'UML:Generalization' => \&uml_generalization,
                        'UML:TaggedValue' => \&uml_taggedvalue,
                },
            );

[download]

I need to get the value of different tags, but I suspect that I need different handlers for each, depending on the context. For example,

  1. I need to get the name and xmi.id for each class, which I do in uml_class_start() using 
                    my $xmi_id = $elt->att( 'xmi.id' );
                my $name = $elt->att( 'name' );

    [download]
    I don't need any of the UML:TaggedValue tags.
  2. I need the name and xmi.id for each attribute. Getting the name is done in uml_attribute() (which is easy, see the class example, above), but note that the xmi.id is one of the UML:TaggedValue tags (tag="ea_guid").
  3. At the end of the file there are a bunch of UML:TaggedValue tags that are not located within a Class or Attribute block. I need to grab the tag, xmi.id, value (not shown in the XMI snippet), and modelElement values for each (or, more specifically, for a given set of modelElement values). I do that in uml_taggedvalue() using the att() method, as in the class example.

How can I tell XML::Twig to ignore UML::TaggedValue tags in Classes, handle them one way in Attributes, and handle them a different way if they are not in either Classes or Attributes? (There are a couple of additional cases, too, but I can solve those by generalizing the solution to this question.)

Thanks very much, in advance.

In reply to Creating context-specific handlers in XML::Twig by bobf

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