The 'orders' element is a sequence of order elements.

Maybe there aren't any orders, so it could be empty.

That looks something like this:

  <xs:element name="orders">
     <xs:complexType>
        <xs:sequence>
        <xs:element ref="my:order" minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
     </xs:complexType>
  </xs:element>

Note that the 'my' prefix is bound to the targetNamespace value of the schema. This means that the element 'my:order' must be defined in this schema.