public void makeDataFieldCompositeType()
    {
        final EncodedDataType edt = (EncodedDataType)containedTypeByNameMap.get("varData");
        if (edt != null)
        {
            edt.variableLength(true);
        }
    }
Make this composite type, if it has a varData member, variable length
by making the type with the name "varData" be variable length.
sbe-tool/src/main/java/uk/co/real_logic/sbe/xml/CompositeType.java