Question

I can’t figure out how to write DTD for XML file which can contain same elements in mixed order.

Small example which shows the problem is below:

<root>

  <element>
    <one></one>
    <two></two>
  </element>

  <element>
    <two></two>
    <one></one>
  </element>

  <element>
    <two></two>
    <two></two>
    <two></two>
    <two></two>
    <one></one>
    <one></one>
  </element>

</root>

My DTD:

<!ELEMENT root(element*)>
<!ELEMENT element((one*,two*)|(two*,one*))>

I found a similar topic but the solution does not work in my case (and I’m not sure what is wrong with my DTD at the moment).
I get this error message:

xmllint: Content model of Instructors is not determinist: ((one* , two*) | (two* , one*))

Answer 1

<!ELEMENT element (one|two)*>

(Or + if you must have at least one.)