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xml - XSD allowing both simpleType and complexType content for same element?

I have a situation where I have different XMLs that will have different types of properties. Sometimes the element HEADER could have just a node or some XMLs could have elements within the HEADER node and values inside.

Example 1 (HEADER with just text):

<Details HeaderLabel="DETAILS">
   <HEADER Label="Header">2.5%</HEADER>
</Details>

Example 2 (HEADER with two child elements):

<Details HeaderLabel="DETAILS">
   <HEADER Label="Header">
       <HEAD Label="H1a">2.88%</HEAD>
       <HEAD Label="H2b">3.24%</HEAD>
   </HEADER>
</Details>

The XSD works as so: This will validate for example 1:

<xs:element name="HEADER">
   <xs:complexType>
      <xs:simpleContent>
         <xs:extension base="xs:string">
            <xs:attribute name="Label" type="xs:string" use="required" />
          </xs:extension>
       </xs:simpleContent>
    </xs:complexType>
 </xs:element>

This will validate the example 2:

<xs:element name="HEADER">
   <xs:complexType>
      <xs:sequence>
         <xs:element maxOccurs="unbounded" name="HEAD">
           <xs:complexType>
             <xs:simpleContent>
               <xs:extension base="xs:string">
                 <xs:attribute name="Label" type="xs:string" use="required" />
               </xs:extension>
             </xs:simpleContent>
           </xs:complexType>
         </xs:element>
       </xs:sequence>
     <xs:attribute name="Label" type="xs:string" use="required" />
   </xs:complexType>
 </xs:element>

I tried using xs:choice but it didn't seem to work well or maybe I don't have a clear understanding on how to implement choice in this situation.

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In XSD, you cannot allow both simple and complex content unless you're willing to have mix elements and text via mixed="true" (in this case Example 1 is not needed). You could then used XSD 1.1 assertions to exclude both from appearing simultaneously.

<xs:element name="HEADER">
<xs:complexType mixed="true">
  <xs:sequence>
    <xs:element minOccurs="0" maxOccurs="unbounded" name="HEAD">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:string">
            <xs:attribute name="Label" type="xs:string" use="required" />
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
  </xs:sequence>
  <xs:attribute name="Label" type="xs:string" use="required" />
</xs:complexType>
</xs:element>

However, you're swimming against the current here. Instead, accept that you really have two different entities with two different content models and name the different entities differently: SIMPLE_HEADER and COMPLEX_HEADER comes to mind. Then you can use xs:choice/maxOccurs="unbounded" on Details to allow simple and complex headers to be freely interspersed.


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