ItemData - Value versus IsNull example

<!-- Example ItemGroupData demonstrating the use of Value and IsNull -->
<ItemGroupData ItemGroupOID="IG.HEMATOLOGY">
    <!-- Correct use: Value -->
    <ItemGroupData ItemGroupOID="IG.WBC">
        <ItemData ItemOID="IT.WBC">
            <Value>5.2</Value>
        </ItemData>
        <ItemData ItemOID="IT.WBC_UNITS">
            <Value>10*3/uL</Value>
        </ItemData>
    </ItemGroupData>
    <!-- Correct use: IsNull - Value child element must be omitted -->
    <ItemGroupData ItemGroupOID="IT.RBC">
        <ItemData ItemOID="IT.RBC" IsNull="Yes"/>
    </ItemGroupData>
    <!-- INVALID use: both "Value" and "IsNull" are present -->
    <ItemGroupData ItemGroupOID="IT.RBC">
        <ItemData ItemOID="IT.RBC" IsNull="Yes">
            <Value>5.0</Value>
        </ItemData>
        <ItemData ItemOID="IT.RBC_UNITS">
            <Value>10*6/uL</Value>
        </ItemData>
    </ItemGroupData>
</ItemGroupData>