I have an xml document in which elements are hierarchically related to
eachother conceptually.  Unfortunately, the hierarchical relationship
is not modelled in the schema (i.e., the elements are "flattened" in
the document".  I have a case in which I want to remove a high level
element using xslt and want all the related lower-level elements to be
removed as well. Is there an easy way to do this in a template?

For example, imagine a relationship of elements describing animals
starting with "animal" at the top of the hierarchy and ending in "pets"
at the bottom:

animal => class => beastie => breed => pet

Given the xml below, say I wanted to remove the class named "Aves" and
wanted  to cause a cascading removal of all other elements related to
"Aves".  Is there a simple way to do this using xsl that helps me avoid
writing specific templates for each child node of "animals"?

<?xml version="1.0" encoding="utf-8"?>
<animals>

   <classes>
      <class name="Mammalia"/>
      <class name="Aves"/>
   </classes>

   <beasties>
      <beast type="cat" class="Mammalia"/>
      <beast type="dog" class="Mammalia"/>
      <beast type="bird" class="Aves"/>
   </beasties>

   <breeds>
      <breed name="collie" type="dog"/>
      <breed name="beagle" type="dog"/>
      <breed name="persian" type="cat"/>
      <breed name="siamese" type="cat"/>
      <breed name="parakeet" type="bird"/>
      <breed name="crow" type="bird"/>
   </breeds>

   <pets>
      <pet name="rover" breed="collie"/>
      <pet name="fluffy" breed="persian"/>
      <pet name="tweety" breed="parakeet"/>
   </pets>

</animals>

The desired xml output would be this:

<?xml version="1.0" encoding="utf-8"?>
<animals>

   <classes>
      <class name="Mammalia"/>
   </classes>

   <beasties>
      <beast type="cat" class="Mammalia"/>
      <beast type="dog" class="Mammalia"/>
   </beasties>

   <breeds>
      <breed name="collie" type="dog"/>
      <breed name="beagle" type="dog"/>
      <breed name="persian" type="cat"/>
      <breed name="siamese" type="cat"/>
   </breeds>

   <pets>
      <pet name="rover" breed="collie"/>
      <pet name="fluffy" breed="persian"/>
   </pets>

</animals>