How to define DTD without strict element order?

As an XML "n开发者_运维百科oob" I have discovered the importance of element order when creating an XML stream/file that is validated against a DTD. Is it possible to define a DTD that is not order dependent on elements ? If, so please provide syntactic example.

You use or (a vertical pipe) and repeat (an asterisk:)

<!ELEMENT eltype1 ( eltype2 | eltype3)*>

This means eltype1 can contain any number of repetitions of eltype2 or eltype3.

The only issue with the currently accepted answer is that it doesn't force only one of each element in any order. For example, you could have 2 eltype2 elements and no eltype3 elements.

If you need to be sure that both elements are present and that each occurs only one time, this is a more precise element declaration:

<!ELEMENT eltype1 ((eltype2, eltype3)|(eltype3, eltype2))>

Example in an internal subset:

<!DOCTYPE eltype1 [
<!ELEMENT eltype1 ((eltype2, eltype3)|(eltype3, eltype2))>
<!ELEMENT eltype2 (#PCDATA)>
<!ELEMENT eltype3 (#PCDATA)>
]>
<eltype1>
  <eltype3>element three</eltype3>
  <eltype2>element two</eltype2>
</eltype1>