Tôi đã tự tìm ra.
Sự khác biệt giữa các ví dụ của tôi không rõ ràng ngay từ cái nhìn đầu tiên, nhưng nếu ví dụ này phức tạp hơn một chút thì nó sẽ có ý nghĩa.
Việc gia hạn sau đây làm rõ sự khác biệt:
<xsd:element name="XList">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="X" type="xsd:token"
minOccurs="1" maxOccurs="1"/>
<xsd:element name="Y" type="xsd:token"
minOccurs="1" maxOccurs="1"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
dẫn đến
<XList>
<X>Only X</X>
<Y>Only Y</Y>
</XList>
trong khi
<xsd:element name="XList">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="X" type="xsd:token"
minOccurs="1" maxOccurs="unbounded"/>
<xsd:element name="Y" type="xsd:token"
minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
dẫn đến
<XList>
<X>First X</X>
<X>Second X</X>
<X>Third X</X>
...
<Y>First Y</Y>
<Y>Second Y</Y>
...
</XList>
và
<xsd:element name="XList">
<xsd:complexType>
<xsd:sequence minOccurs="1" maxOccurs="unbounded" >
<xsd:element name="X" type="xsd:token"
minOccurs="2" maxOccurs="2"/>
<xsd:element name="Y" type="xsd:token"
minOccurs="1" maxOccurs="1"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
dẫn đến
<XList>
<X>First X</X>
<X>Second X</X>
<Y>First Y</Y>
<X>Third X</X>
<X>Fourth X</X>
<Y>Second Y</Y>
...
</XList>
và
<xsd:element name="XList">
<xsd:complexType>
<xsd:sequence minOccurs="1" maxOccurs="unbounded" >
<xsd:element name="X" type="xsd:token"
minOccurs="1" maxOccurs="unbounded"/>
<xsd:element name="Y" type="xsd:token"
minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
dẫn đến
<XList>
<X>First X</X>
<X>Second X</X>
<X>Third X</X>
...
<Y>First Y</Y>
<Y>Second Y</Y>
...
<X>Fourth X</X>
<X>Fifth X</X>
<X>Sixth X</X>
...
<Y>Third Y</Y>
<Y>Fourth Y</Y>
...
</XList>