xsd: define an element that can be repeated an even number of times

问题

with xsd, is there a way in which we can define an element that is repeated an even number of times? with my information it is not possible with the attributes minOcurs and maxOccurs.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" >
<xs:element name="A">
  <xs:complexType>
      <xs:sequence>
          <xs:element name="B" maxOccurs="?" minOccurs="?"/>
      </xs:sequence>
  </xs:complexType>  
</xs:element>
</xs:schema>

回答1:

How about this:

  <xs:sequence minOccurs="0" maxOccurs="unbounded">
      <xs:element name="B" maxOccurs="2" minOccurs="2"/>
  </xs:sequence>

来源：https://stackoverflow.com/questions/27192211/xsd-define-an-element-that-can-be-repeated-an-even-number-of-times