TextureBackgroundChildContentModel

<xs:group name="TextureBackgroundChildContentModel">
  <xs:annotation>
    <xs:appinfo>TextureBackgroundChildContentModel is the child-node content model utilized by TextureBackground. TextureBackgroundChildContentModel can contain up to six Texture nodes (ImageTexture, MovieTexture, MultiTexture or PixelTexture). Each child texture shall have a different containerField for topTexture, bottomTexture, leftTexture, rightTexture, frontTexture and backTexture.</xs:appinfo>
    <xs:documentation source="http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/enveffects.html#TextureBackground"/>
  </xs:annotation>
  <xs:choice>
    <xs:element ref="ImageTexture"/>
    <xs:element ref="MovieTexture"/>
    <xs:element ref="MultiTexture"/>
    <xs:element ref="PixelTexture"/>
    <xs:element ref="ProtoInstance">
      <xs:annotation>
        <xs:documentation>Appropriately typed substitution node</xs:documentation>
      </xs:annotation>
    </xs:element>
  </xs:choice>
  <!--Controversial construct, throws errors if includes minOccurs="0" maxOccurs="6".  Deterministic content model.
		Moved constraint to parent referring xs:group OK.  Still need to test if more than 6 children will be invalidated.-->
</xs:group>