Sorry if this is a newbie question.  I couldn't get the correct magic
incantation for Google to get an answer.  :-(

I'm trying to satisfy a requirement that "at least one of the following
*must* be present" in an XML Schema.  I have come up with two examples
that almost work.

Here's the first:

<xs:element name="LightExample1" maxOccurs="3">
   <xs:complexType>
      <xs:choice>
         <xs:element name="A"/>
         <xs:element name="B"/>
         <xs:element name="C"/>
      </xs:choice>
   </xs:complexType>
</xs:element>

This doesn't work because it allows multiple A, B, or C elements.

Here's the second example:

<xs:element name="LightExample2">
   <xs:complexType>
      <xs:sequence>
         <xs:element name="A" minOccurs="0"/>
         <xs:element name="B" minOccurs="0"/>
         <xs:element name="C" minOccurs="0"/>
      </xs:sequence>
   </xs:complexType>
</xs:element>

This *almost* works.  The only problem is that it allows an empty
<LightExample2/> element which fails the "at least one of" portion of
the requirement.

Is it possible to do this?

Kenneth