How to validate?

Dear XML Schema Gurus,

Below is an XML fragment:

<location>
 <tourist>
  <ID></ID>
  <PassPortNo></PassPortNo>
  <Nation></Nation>
 </tourist>
</location>

How can I do the following validations?
1.either ID or PassPortNo should be filled in
2.Nation should have value(not including space)
3.ID should have either 10 or 11 characters

Grateful if you can help!

Carter



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