The following is Paul Biron's translation of the original comment (which was in 
French): 

Allow me make a small comment regarding the XML Schema Part 0: Introduction 
available at the URL http://xmlfr.org/w3c/TR/xmlschema-0/.

In Chapter 2.2, one can read (just after the definition of the type 
USAddress) "The consequence of this definition is that all instances of this 
element in an instance (for example shipTo in the file po.xml) must consist of 
5 elements and one attribute. 

Also in the same chapter 2.2 (just after the definition of the type 
PurchaseOrderType): "The elements shipTo and billTo may equally have a country 
attribute which is part of the definition of USAddress." 

In the first case shipTo MUST have the attribute, in the second case, shipTo 
MAY have the attribute. This is a X significant difference [trans: I can't find 
a translation of reelle...it might be a typo] . (I have seen the English 
version, and it has the same ambiguity). 

See:
http://lists.w3.org/Archives/Public/www-xml-schema-comments/2003JanMar/0076.html