title: XML Validation for any element order with specific count ranges
body: <p>I'm trying to find a way to write an XML 1.0 schema that avoids creating an untenable number permutations.  I have 5 elements, A, B, C, D, and E. A must occur exactly once in the XML. B and C can occur 0 to infinity times in the XML. D and E can occur 1 to infinity times in the XML. A-E can occur in any order.</p>
  
  <p>It's important to avoid writing out each possible sequence because if I need to add an element later the schema grows exponentially. Is there a way to do this?</p>