Hi,

I'm relatively new to XSD but I did not think that my requirement would 
prove to be such a problem. But after two hours of trying and searching 
I'm now thoroughly confused. Maybe someone could point me into the right 
direction.

Requirement: There are three elements. One is optional, while the other 
two are exclusively to each other. One of the latter might appear 
multiple times.

Therefore, I wrote the following XSD, which is working perfectly:

<xs:element name="Root">
   <xs:complexType>
     <xs:sequence>
       <xs:choice>
         <xs:element name="One" type="xs:string" maxOccurs="unbounded" />
         <xs:element name="Two" type="xs:string" />
       </xs:choice>
       <xs:element name="Description" type="xs:string" minOccurs="0" />
     </xs:sequence>
   </xs:complexType>
</xs:element>

It allows <One> multiple times OR <Two> once and <Description> is 
optional. The problem I can't get my head around is how to achieve that 
the order of the choice group and the description tag is irrelevant. 
<Description> should be allowed to occur first.

All my attempts to do that have failed. I'm not allowed to use <all> 
instead of <sequence>, because <all> is only allowed to contain 
elements. And if I replace the <sequence> with an

<xs:choice maxOccurs="unbounded">

the order is no longer relevant, but also an *empty* XML document is now 
valid (which had me surprised for a moment, but I think I understand it 
now).

I'm completely in the dark on how to achieve my additional requirement. 
Specifying all possible permutations in a choice of sequences is 
obviously no solution, since I need a lot more elements in the final 
XSD. It seems simple to me but I can't get it to work, so any help would 
be greatly appreciated.

tia, stephan