I was very impressed when I saw how Subversion handles the complexity of having data of hierarchical nature that needs to be serialized to XML. Check this out.

<?xml version="1.0" encoding="utf-8"?>
<S:editor-report xmlns:S="svn:">
  <S:target-revision rev="11"/>
  <S:open-root rev="-1"/>
  <S:open-directory name="tags" rev="-1"/>
  <S:add-directory name="tags/asd"/>
  <S:close-directory/>
  <S:close-directory/>
  <S:close-directory/>
</S:editor-report>

And here is another one:

<?xml version="1.0" encoding="utf-8"?>
<S:editor-report xmlns:S="svn:">
  <S:target-revision rev="15"/>
  <S:open-root rev="-1"/>
  <S:open-directory name="trunk" rev="-1"/>
  <S:open-file name="trunk/a.txt" rev="-1"/>
  <S:apply-textdelta checksum="eabc96676e7defda414a1eed33bdfb09">
    U1ZOAAAQEwETk2FzZDENCjINCjMNCjQNCjUNCjY=
  </S:apply-textdelta>
  <S:close-file checksum="c6301e5dad1330a7b9bd5491702c801b"/>
  <S:close-directory/>
  <S:close-directory/>
</S:editor-report>

I was, as they say incredibly happy with this Work Time Fun.