I'm not aware of attribute order ever being a concern. Element order always is so in the following code, you must always reconstruct it in this order. The two identically named elements may remain in order though DTD doesn't require it. The other sibling elements D and C must remain in exactly that order - perl's hash order cannot be allowed to disturb that. All in all, I think you'll find that Tie::HashIx is useful for this. If you don't intend on producing validatable XML then this requirement isn't important - your call.

<a>
  <d>e</d>

  <b>a</b>
  <b>b</b>

  <c>c</c>
</a>
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